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 $111.77   11.277%   $124.3743   $124.37   $124.35   $124.40  
  Purchase #2 $85.37   10.868%   $94.648   $94.65   $94.65   $94.60  
  Purchase #3 $61.62   10.665%   $68.1918   $68.19   $68.20   $68.20  
  Purchase #4 $85.51   3.484%   $88.4892   $88.49   $88.50   $88.50  
  Purchase #5 $191.63   5.654%   $202.4648   $202.46   $202.45   $202.50  
  Purchase #6 $54.28   9.674%   $59.531   $59.53   $59.55   $59.50  
  Purchase #7 $110.64   13.126%   $125.1626   $125.16   $125.15   $125.20  
  7 purchase totals = $700.82       $762.8617   $762.85   $762.85   $762.90