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 $241.76   9.731%   $265.2857   $265.29   $265.30   $265.30  
  Purchase #2 $144.78   7.393%   $155.4836   $155.48   $155.50   $155.50  
  Purchase #3 $67.55   12.658%   $76.1005   $76.10   $76.10   $76.10  
  Purchase #4 $125.41   8.872%   $136.5364   $136.54   $136.55   $136.50  
  Purchase #5 $115.35   9.360%   $126.1468   $126.15   $126.15   $126.10  
  Purchase #6 $77.80   11.761%   $86.9501   $86.95   $86.95   $87.00  
  Purchase #7 $127.35   7.285%   $136.6274   $136.63   $136.65   $136.60  
  7 purchase totals = $900.00       $983.1305   $983.14   $983.20   $983.10