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 $206.43   11.179%   $229.5068   $229.51   $229.50   $229.50  
  Purchase #2 $228.56   13.341%   $259.0522   $259.05   $259.05   $259.10  
  Purchase #3 $236.89   11.519%   $264.1774   $264.18   $264.20   $264.20  
  Purchase #4 $211.54   6.457%   $225.1991   $225.20   $225.20   $225.20  
  Purchase #5 $33.62   11.813%   $37.5915   $37.59   $37.60   $37.60  
  Purchase #6 $208.65   5.617%   $220.3699   $220.37   $220.35   $220.40  
  Purchase #7 $245.63   8.391%   $266.2408   $266.24   $266.25   $266.20  
  7 purchase totals = $1,371.32       $1,502.1377   $1,502.14   $1,502.15   $1,502.20