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 $162.95   13.463%   $184.888   $184.89   $184.90   $184.90  
  Purchase #2 $119.34   7.784%   $128.6294   $128.63   $128.65   $128.60  
  Purchase #3 $88.91   5.477%   $93.7796   $93.78   $93.80   $93.80  
  Purchase #4 $16.79   8.491%   $18.2156   $18.22   $18.20   $18.20  
  Purchase #5 $241.57   12.614%   $272.0416   $272.04   $272.05   $272.00  
  Purchase #6 $6.46   6.501%   $6.88   $6.88   $6.90   $6.90  
  Purchase #7 $195.86   7.766%   $211.0705   $211.07   $211.05   $211.10  
  7 purchase totals = $831.88       $915.5047   $915.51   $915.55   $915.50