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 $189.73   9.141%   $207.0732   $207.07   $207.05   $207.10  
  Purchase #2 $129.27   13.536%   $146.768   $146.77   $146.75   $146.80  
  Purchase #3 $93.58   12.670%   $105.4366   $105.44   $105.45   $105.40  
  Purchase #4 $120.56   4.269%   $125.7067   $125.71   $125.70   $125.70  
  Purchase #5 $88.84   12.578%   $100.0143   $100.01   $100.00   $100.00  
  Purchase #6 $94.94   3.753%   $98.5031   $98.50   $98.50   $98.50  
  Purchase #7 $182.63   4.262%   $190.4137   $190.41   $190.40   $190.40  
  7 purchase totals = $899.55       $973.9156   $973.91   $973.85   $973.90