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 $205.97   11.663%   $229.9923   $229.99   $230.00   $230.00  
  Purchase #2 $86.65   10.366%   $95.6321   $95.63   $95.65   $95.60  
  Purchase #3 $125.65   3.214%   $129.6884   $129.69   $129.70   $129.70  
  Purchase #4 $217.47   8.786%   $236.5769   $236.58   $236.60   $236.60  
  Purchase #5 $217.93   8.453%   $236.3516   $236.35   $236.35   $236.40  
  Purchase #6 $110.56   7.654%   $119.0223   $119.02   $119.00   $119.00  
  Purchase #7 $51.97   11.443%   $57.9169   $57.92   $57.90   $57.90  
  7 purchase totals = $1,016.20       $1,105.1805   $1,105.18   $1,105.20   $1,105.20