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 $22.93   13.694%   $26.07   $26.07   $26.05   $26.10  
  Purchase #2 $176.84   11.106%   $196.4799   $196.48   $196.50   $196.50  
  Purchase #3 $24.38   5.392%   $25.6946   $25.69   $25.70   $25.70  
  Purchase #4 $234.52   4.138%   $244.2244   $244.22   $244.20   $244.20  
  Purchase #5 $88.71   4.226%   $92.4589   $92.46   $92.45   $92.50  
  Purchase #6 $161.61   5.687%   $170.8008   $170.80   $170.80   $170.80  
  Purchase #7 $170.52   8.696%   $185.3484   $185.35   $185.35   $185.30  
  7 purchase totals = $879.51       $941.0770   $941.07   $941.05   $941.10