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 $207.29   8.317%   $224.5303   $224.53   $224.55   $224.50  
  Purchase #2 $126.68   7.584%   $136.2874   $136.29   $136.30   $136.30  
  Purchase #3 $35.42   3.151%   $36.5361   $36.54   $36.55   $36.50  
  Purchase #4 $66.39   6.734%   $70.8607   $70.86   $70.85   $70.90  
  Purchase #5 $59.42   3.706%   $61.6221   $61.62   $61.60   $61.60  
  Purchase #6 $174.80   5.788%   $184.9174   $184.92   $184.90   $184.90  
  Purchase #7 $77.51   12.350%   $87.0825   $87.08   $87.10   $87.10  
  7 purchase totals = $747.51       $801.8365   $801.84   $801.85   $801.80