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 $88.71   6.581%   $94.548   $94.55   $94.55   $94.50  
  Purchase #2 $9.28   4.303%   $9.6793   $9.68   $9.70   $9.70  
  Purchase #3 $170.80   9.286%   $186.6605   $186.66   $186.65   $186.70  
  Purchase #4 $103.48   12.848%   $116.7751   $116.78   $116.80   $116.80  
  Purchase #5 $86.67   4.495%   $90.5658   $90.57   $90.55   $90.60  
  Purchase #6 $52.87   11.439%   $58.9178   $58.92   $58.90   $58.90  
  Purchase #7 $126.76   11.546%   $141.3957   $141.40   $141.40   $141.40  
  7 purchase totals = $638.57       $698.5422   $698.56   $698.55   $698.60