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 $241.26   5.793%   $255.2362   $255.24   $255.25   $255.20  
  Purchase #2 $207.73   3.814%   $215.6528   $215.65   $215.65   $215.70  
  Purchase #3 $122.97   7.571%   $132.2801   $132.28   $132.30   $132.30  
  Purchase #4 $221.98   12.838%   $250.4778   $250.48   $250.50   $250.50  
  Purchase #5 $181.53   12.836%   $204.8312   $204.83   $204.85   $204.80  
  Purchase #6 $158.53   12.506%   $178.3558   $178.36   $178.35   $178.40  
  Purchase #7 $13.42   12.306%   $15.0715   $15.07   $15.05   $15.10  
  7 purchase totals = $1,147.42       $1,251.9054   $1,251.91   $1,251.95   $1,252.00