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 $109.77   13.855%   $124.9786   $124.98   $125.00   $125.00  
  Purchase #2 $30.26   10.785%   $33.5235   $33.52   $33.50   $33.50  
  Purchase #3 $61.95   7.399%   $66.5337   $66.53   $66.55   $66.50  
  Purchase #4 $123.33   6.260%   $131.0505   $131.05   $131.05   $131.10  
  Purchase #5 $57.76   6.653%   $61.6028   $61.60   $61.60   $61.60  
  Purchase #6 $44.73   5.577%   $47.2246   $47.22   $47.20   $47.20  
  Purchase #7 $173.60   12.151%   $194.6941   $194.69   $194.70   $194.70  
  7 purchase totals = $601.40       $659.6078   $659.59   $659.60   $659.60