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 $22.36   10.657%   $24.7429   $24.74   $24.75   $24.70  
  Purchase #2 $31.69   12.751%   $35.7308   $35.73   $35.75   $35.70  
  Purchase #3 $125.35   5.160%   $131.8181   $131.82   $131.80   $131.80  
  Purchase #4 $235.46   11.573%   $262.7098   $262.71   $262.70   $262.70  
  Purchase #5 $163.81   8.586%   $177.8747   $177.87   $177.85   $177.90  
  Purchase #6 $83.52   12.748%   $94.1671   $94.17   $94.15   $94.20  
  Purchase #7 $168.88   4.393%   $176.2989   $176.30   $176.30   $176.30  
  7 purchase totals = $831.07       $903.3423   $903.34   $903.30   $903.30