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 $58.33   6.617%   $62.1897   $62.19   $62.20   $62.20  
  Purchase #2 $88.88   6.540%   $94.6928   $94.69   $94.70   $94.70  
  Purchase #3 $182.97   10.121%   $201.4884   $201.49   $201.50   $201.50  
  Purchase #4 $87.74   10.796%   $97.2124   $97.21   $97.20   $97.20  
  Purchase #5 $90.64   12.426%   $101.9029   $101.90   $101.90   $101.90  
  Purchase #6 $5.75   9.196%   $6.2788   $6.28   $6.30   $6.30  
  Purchase #7 $55.25   6.869%   $59.0451   $59.05   $59.05   $59.00  
  7 purchase totals = $569.56       $622.8101   $622.81   $622.85   $622.80