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 $117.77   5.486%   $124.2309   $124.23   $124.25   $124.20  
  Purchase #2 $13.31   13.481%   $15.1043   $15.10   $15.10   $15.10  
  Purchase #3 $190.60   6.362%   $202.726   $202.73   $202.75   $202.70  
  Purchase #4 $161.97   7.742%   $174.5097   $174.51   $174.50   $174.50  
  Purchase #5 $161.79   10.629%   $178.9867   $178.99   $179.00   $179.00  
  Purchase #6 $47.41   11.491%   $52.8579   $52.86   $52.85   $52.90  
  Purchase #7 $205.90   5.437%   $217.0948   $217.09   $217.10   $217.10  
  7 purchase totals = $898.75       $965.5103   $965.51   $965.55   $965.50