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 $208.59   7.424%   $224.0757   $224.08   $224.10   $224.10  
  Purchase #2 $232.31   12.502%   $261.3534   $261.35   $261.35   $261.40  
  Purchase #3 $131.61   11.477%   $146.7149   $146.71   $146.70   $146.70  
  Purchase #4 $194.99   13.503%   $221.3195   $221.32   $221.30   $221.30  
  Purchase #5 $65.71   6.731%   $70.1329   $70.13   $70.15   $70.10  
  Purchase #6 $177.37   3.313%   $183.2463   $183.25   $183.25   $183.20  
  Purchase #7 $234.99   13.487%   $266.6831   $266.68   $266.70   $266.70  
  7 purchase totals = $1,245.57       $1,373.5258   $1,373.52   $1,373.55   $1,373.50