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 $126.33   8.401%   $136.943   $136.94   $136.95   $136.90  
  Purchase #2 $106.47   13.296%   $120.6263   $120.63   $120.65   $120.60  
  Purchase #3 $24.96   12.743%   $28.1407   $28.14   $28.15   $28.10  
  Purchase #4 $87.41   11.474%   $97.4394   $97.44   $97.45   $97.40  
  Purchase #5 $155.57   11.785%   $173.9039   $173.90   $173.90   $173.90  
  Purchase #6 $160.45   5.672%   $169.5507   $169.55   $169.55   $169.60  
  Purchase #7 $24.51   6.867%   $26.1931   $26.19   $26.20   $26.20  
  7 purchase totals = $685.70       $752.7971   $752.79   $752.85   $752.70