Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $50.43   3.446%   $52.1678   $52.17   $52.15   $52.20  
  Purchase #2 $70.25   8.632%   $76.314   $76.31   $76.30   $76.30  
  Purchase #3 $84.93   13.805%   $96.6546   $96.65   $96.65   $96.70  
  Purchase #4 $250.99   4.495%   $262.272   $262.27   $262.25   $262.30  
  Purchase #5 $156.61   6.628%   $166.9901   $166.99   $167.00   $167.00  
  Purchase #6 $184.35   11.199%   $204.9954   $205.00   $205.00   $205.00  
  Purchase #7 $180.99   5.157%   $190.3237   $190.32   $190.30   $190.30  
  7 purchase totals = $978.55       $1,049.7176   $1,049.71   $1,049.65   $1,049.80