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 $68.35   8.113%   $73.8952   $73.90   $73.90   $73.90  
  Purchase #2 $56.96   12.836%   $64.2714   $64.27   $64.25   $64.30  
  Purchase #3 $72.59   3.567%   $75.1793   $75.18   $75.20   $75.20  
  Purchase #4 $63.47   5.239%   $66.7952   $66.80   $66.80   $66.80  
  Purchase #5 $52.58   7.655%   $56.605   $56.61   $56.60   $56.60  
  Purchase #6 $146.34   7.690%   $157.5935   $157.59   $157.60   $157.60  
  Purchase #7 $46.26   13.774%   $52.6319   $52.63   $52.65   $52.60  
  7 purchase totals = $506.55       $546.9715   $546.98   $547.00   $547.00