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 $236.36   12.491%   $265.8837   $265.88   $265.90   $265.90  
  Purchase #2 $53.97   12.580%   $60.7594   $60.76   $60.75   $60.80  
  Purchase #3 $197.71   3.738%   $205.1004   $205.10   $205.10   $205.10  
  Purchase #4 $51.44   4.335%   $53.6699   $53.67   $53.65   $53.70  
  Purchase #5 $217.31   4.659%   $227.4345   $227.43   $227.45   $227.40  
  Purchase #6 $85.45   8.599%   $92.7978   $92.80   $92.80   $92.80  
  Purchase #7 $234.57   4.873%   $246.0006   $246.00   $246.00   $246.00  
  7 purchase totals = $1,076.81       $1,151.6463   $1,151.64   $1,151.65   $1,151.70