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 $59.53   11.519%   $66.3873   $66.39   $66.40   $66.40  
  Purchase #2 $223.96   9.127%   $244.4008   $244.40   $244.40   $244.40  
  Purchase #3 $32.47   10.645%   $35.9264   $35.93   $35.95   $35.90  
  Purchase #4 $84.37   9.268%   $92.1894   $92.19   $92.20   $92.20  
  Purchase #5 $104.49   3.431%   $108.0751   $108.08   $108.10   $108.10  
  Purchase #6 $215.91   12.189%   $242.2273   $242.23   $242.25   $242.20  
  Purchase #7 $68.27   3.367%   $70.5687   $70.57   $70.55   $70.60  
  7 purchase totals = $789.00       $859.7750   $859.79   $859.85   $859.80