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 $41.72   10.614%   $46.1482   $46.15   $46.15   $46.10  
  Purchase #2 $166.62   4.262%   $173.7213   $173.72   $173.70   $173.70  
  Purchase #3 $103.86   6.573%   $110.6867   $110.69   $110.70   $110.70  
  Purchase #4 $141.65   3.373%   $146.4279   $146.43   $146.45   $146.40  
  Purchase #5 $63.73   4.491%   $66.5921   $66.59   $66.60   $66.60  
  Purchase #6 $65.78   11.655%   $73.4467   $73.45   $73.45   $73.40  
  Purchase #7 $103.34   3.188%   $106.6345   $106.63   $106.65   $106.60  
  7 purchase totals = $686.70       $723.6574   $723.66   $723.70   $723.50