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 $202.37   5.492%   $213.4842   $213.48   $213.50   $213.50  
  Purchase #2 $86.92   6.175%   $92.2873   $92.29   $92.30   $92.30  
  Purchase #3 $88.90   10.555%   $98.2834   $98.28   $98.30   $98.30  
  Purchase #4 $147.85   6.784%   $157.8801   $157.88   $157.90   $157.90  
  Purchase #5 $139.90   8.156%   $151.3102   $151.31   $151.30   $151.30  
  Purchase #6 $28.48   5.710%   $30.1062   $30.11   $30.10   $30.10  
  Purchase #7 $47.35   8.812%   $51.5225   $51.52   $51.50   $51.50  
  7 purchase totals = $741.77       $794.8739   $794.87   $794.90   $794.90