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 $226.36   13.475%   $256.862   $256.86   $256.85   $256.90  
  Purchase #2 $235.37   10.183%   $259.3377   $259.34   $259.35   $259.30  
  Purchase #3 $227.41   9.585%   $249.2072   $249.21   $249.20   $249.20  
  Purchase #4 $24.77   10.718%   $27.4248   $27.42   $27.40   $27.40  
  Purchase #5 $250.64   13.810%   $285.2534   $285.25   $285.25   $285.30  
  Purchase #6 $226.61   11.188%   $251.9631   $251.96   $251.95   $252.00  
  Purchase #7 $35.55   11.797%   $39.7438   $39.74   $39.75   $39.70  
  7 purchase totals = $1,226.71       $1,369.7920   $1,369.78   $1,369.75   $1,369.80