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 $84.73   13.715%   $96.3507   $96.35   $96.35   $96.40  
  Purchase #2 $118.95   9.114%   $129.7911   $129.79   $129.80   $129.80  
  Purchase #3 $65.83   9.234%   $71.9087   $71.91   $71.90   $71.90  
  Purchase #4 $116.58   12.525%   $131.1816   $131.18   $131.20   $131.20  
  Purchase #5 $232.90   3.815%   $241.7851   $241.79   $241.80   $241.80  
  Purchase #6 $245.28   6.706%   $261.7285   $261.73   $261.75   $261.70  
  Purchase #7 $20.78   8.289%   $22.5025   $22.50   $22.50   $22.50  
  7 purchase totals = $885.05       $955.2482   $955.25   $955.30   $955.30