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 $57.88   12.262%   $64.9772   $64.98   $65.00   $65.00  
  Purchase #2 $49.48   4.425%   $51.6695   $51.67   $51.65   $51.70  
  Purchase #3 $73.53   6.243%   $78.1205   $78.12   $78.10   $78.10  
  Purchase #4 $108.61   11.504%   $121.1045   $121.10   $121.10   $121.10  
  Purchase #5 $215.58   9.430%   $235.9092   $235.91   $235.90   $235.90  
  Purchase #6 $210.78   6.794%   $225.1004   $225.10   $225.10   $225.10  
  Purchase #7 $87.39   10.118%   $96.2321   $96.23   $96.25   $96.20  
  7 purchase totals = $803.25       $873.1134   $873.11   $873.10   $873.10