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 $65.48   3.831%   $67.9885   $67.99   $68.00   $68.00  
  Purchase #2 $44.71   10.722%   $49.5038   $49.50   $49.50   $49.50  
  Purchase #3 $79.92   5.754%   $84.5186   $84.52   $84.50   $84.50  
  Purchase #4 $51.81   7.601%   $55.7481   $55.75   $55.75   $55.70  
  Purchase #5 $119.50   5.341%   $125.8825   $125.88   $125.90   $125.90  
  Purchase #6 $102.27   7.525%   $109.9658   $109.97   $109.95   $110.00  
  Purchase #7 $13.27   5.833%   $14.044   $14.04   $14.05   $14.00  
  7 purchase totals = $476.96       $507.6513   $507.65   $507.65   $507.60