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 $118.94   5.272%   $125.2105   $125.21   $125.20   $125.20  
  Purchase #2 $23.45   11.693%   $26.192   $26.19   $26.20   $26.20  
  Purchase #3 $38.31   5.697%   $40.4925   $40.49   $40.50   $40.50  
  Purchase #4 $59.31   8.867%   $64.569   $64.57   $64.55   $64.60  
  Purchase #5 $197.26   12.422%   $221.7636   $221.76   $221.75   $221.80  
  Purchase #6 $31.39   12.515%   $35.3185   $35.32   $35.30   $35.30  
  Purchase #7 $182.59   11.762%   $204.0662   $204.07   $204.05   $204.10  
  7 purchase totals = $651.25       $717.6123   $717.61   $717.55   $717.70