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 $58.35   3.513%   $60.3998   $60.40   $60.40   $60.40  
  Purchase #2 $146.99   4.230%   $153.2077   $153.21   $153.20   $153.20  
  Purchase #3 $119.87   4.589%   $125.3708   $125.37   $125.35   $125.40  
  Purchase #4 $26.96   6.469%   $28.704   $28.70   $28.70   $28.70  
  Purchase #5 $96.75   5.505%   $102.0761   $102.08   $102.10   $102.10  
  Purchase #6 $118.62   11.159%   $131.8568   $131.86   $131.85   $131.90  
  Purchase #7 $189.88   12.554%   $213.7175   $213.72   $213.70   $213.70  
  7 purchase totals = $757.42       $815.3327   $815.34   $815.30   $815.40