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 $225.28   8.162%   $243.6674   $243.67   $243.65   $243.70  
  Purchase #2 $213.88   6.427%   $227.6261   $227.63   $227.65   $227.60  
  Purchase #3 $61.28   11.715%   $68.459   $68.46   $68.45   $68.50  
  Purchase #4 $106.78   5.140%   $112.2685   $112.27   $112.25   $112.30  
  Purchase #5 $17.84   6.793%   $19.0519   $19.05   $19.05   $19.10  
  Purchase #6 $204.25   11.386%   $227.5059   $227.51   $227.50   $227.50  
  Purchase #7 $75.58   11.731%   $84.4463   $84.45   $84.45   $84.40  
  7 purchase totals = $904.89       $983.0251   $983.04   $983.00   $983.10