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 $30.88   8.486%   $33.5005   $33.50   $33.50   $33.50  
  Purchase #2 $120.92   5.277%   $127.3009   $127.30   $127.30   $127.30  
  Purchase #3 $201.27   7.750%   $216.8684   $216.87   $216.85   $216.90  
  Purchase #4 $63.49   6.832%   $67.8276   $67.83   $67.85   $67.80  
  Purchase #5 $125.63   8.433%   $136.2244   $136.22   $136.20   $136.20  
  Purchase #6 $249.65   4.219%   $260.1827   $260.18   $260.20   $260.20  
  Purchase #7 $229.67   4.702%   $240.4691   $240.47   $240.45   $240.50  
  7 purchase totals = $1,021.51       $1,082.3736   $1,082.37   $1,082.35   $1,082.40