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 $21.71   3.716%   $22.5167   $22.52   $22.50   $22.50  
  Purchase #2 $221.49   10.387%   $244.4962   $244.50   $244.50   $244.50  
  Purchase #3 $106.51   10.588%   $117.7873   $117.79   $117.80   $117.80  
  Purchase #4 $49.54   5.765%   $52.396   $52.40   $52.40   $52.40  
  Purchase #5 $83.87   12.461%   $94.321   $94.32   $94.30   $94.30  
  Purchase #6 $158.72   9.508%   $173.8111   $173.81   $173.80   $173.80  
  Purchase #7 $24.51   7.647%   $26.3843   $26.38   $26.40   $26.40  
  7 purchase totals = $666.35       $731.7126   $731.72   $731.70   $731.70