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 $84.38   9.817%   $92.6636   $92.66   $92.65   $92.70  
  Purchase #2 $62.78   12.384%   $70.5547   $70.55   $70.55   $70.60  
  Purchase #3 $188.78   13.360%   $214.001   $214.00   $214.00   $214.00  
  Purchase #4 $92.47   9.618%   $101.3638   $101.36   $101.35   $101.40  
  Purchase #5 $149.57   11.582%   $166.8932   $166.89   $166.90   $166.90  
  Purchase #6 $52.92   12.633%   $59.6054   $59.61   $59.60   $59.60  
  Purchase #7 $186.34   12.719%   $210.0406   $210.04   $210.05   $210.00  
  7 purchase totals = $817.24       $915.1223   $915.11   $915.10   $915.20