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 $23.26   11.628%   $25.9647   $25.96   $25.95   $26.00  
  Purchase #2 $248.83   3.648%   $257.9073   $257.91   $257.90   $257.90  
  Purchase #3 $87.56   6.544%   $93.2899   $93.29   $93.30   $93.30  
  Purchase #4 $199.55   6.340%   $212.2015   $212.20   $212.20   $212.20  
  Purchase #5 $88.93   11.549%   $99.2005   $99.20   $99.20   $99.20  
  Purchase #6 $183.30   6.248%   $194.7526   $194.75   $194.75   $194.80  
  Purchase #7 $42.92   5.541%   $45.2982   $45.30   $45.30   $45.30  
  7 purchase totals = $874.35       $928.6147   $928.61   $928.60   $928.70