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 $144.54   13.259%   $163.7046   $163.70   $163.70   $163.70  
  Purchase #2 $221.74   7.629%   $238.6565   $238.66   $238.65   $238.70  
  Purchase #3 $22.77   8.689%   $24.7485   $24.75   $24.75   $24.70  
  Purchase #4 $30.46   9.547%   $33.368   $33.37   $33.35   $33.40  
  Purchase #5 $115.47   4.764%   $120.971   $120.97   $120.95   $121.00  
  Purchase #6 $73.81   8.171%   $79.841   $79.84   $79.85   $79.80  
  Purchase #7 $83.45   11.697%   $93.2111   $93.21   $93.20   $93.20  
  7 purchase totals = $692.24       $754.5007   $754.50   $754.45   $754.50