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 $54.53   10.369%   $60.1842   $60.18   $60.20   $60.20  
  Purchase #2 $20.63   10.198%   $22.7338   $22.73   $22.75   $22.70  
  Purchase #3 $238.84   3.618%   $247.4812   $247.48   $247.50   $247.50  
  Purchase #4 $59.98   6.827%   $64.0748   $64.07   $64.05   $64.10  
  Purchase #5 $154.44   6.146%   $163.9319   $163.93   $163.95   $163.90  
  Purchase #6 $200.32   11.848%   $224.0539   $224.05   $224.05   $224.10  
  Purchase #7 $240.73   8.351%   $260.8334   $260.83   $260.85   $260.80  
  7 purchase totals = $969.47       $1,043.2932   $1,043.27   $1,043.35   $1,043.30