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 $51.47   4.819%   $53.9503   $53.95   $53.95   $54.00  
  Purchase #2 $181.47   3.721%   $188.2225   $188.22   $188.20   $188.20  
  Purchase #3 $59.33   5.620%   $62.6643   $62.66   $62.65   $62.70  
  Purchase #4 $99.37   11.193%   $110.4925   $110.49   $110.50   $110.50  
  Purchase #5 $77.69   7.842%   $83.7824   $83.78   $83.80   $83.80  
  Purchase #6 $161.53   13.662%   $183.5982   $183.60   $183.60   $183.60  
  Purchase #7 $109.57   8.605%   $118.9985   $119.00   $119.00   $119.00  
  7 purchase totals = $740.43       $801.7087   $801.70   $801.70   $801.80