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 $56.96   4.630%   $59.5972   $59.60   $59.60   $59.60  
  Purchase #2 $136.55   7.415%   $146.6752   $146.68   $146.70   $146.70  
  Purchase #3 $250.98   8.674%   $272.75   $272.75   $272.75   $272.80  
  Purchase #4 $84.40   9.248%   $92.2053   $92.21   $92.20   $92.20  
  Purchase #5 $35.74   7.828%   $38.5377   $38.54   $38.55   $38.50  
  Purchase #6 $196.50   13.860%   $223.7349   $223.73   $223.75   $223.70  
  Purchase #7 $119.85   4.709%   $125.4937   $125.49   $125.50   $125.50  
  7 purchase totals = $880.98       $958.9940   $959.00   $959.05   $959.00