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 $201.66   5.612%   $212.9772   $212.98   $213.00   $213.00  
  Purchase #2 $37.98   3.271%   $39.2223   $39.22   $39.20   $39.20  
  Purchase #3 $54.66   4.690%   $57.2236   $57.22   $57.20   $57.20  
  Purchase #4 $133.48   5.282%   $140.5304   $140.53   $140.55   $140.50  
  Purchase #5 $140.57   7.438%   $151.0256   $151.03   $151.05   $151.00  
  Purchase #6 $82.32   3.217%   $84.9682   $84.97   $84.95   $85.00  
  Purchase #7 $244.42   8.753%   $265.8141   $265.81   $265.80   $265.80  
  7 purchase totals = $895.09       $951.7614   $951.76   $951.75   $951.70