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 $234.26   13.531%   $265.9577   $265.96   $265.95   $266.00  
  Purchase #2 $183.96   13.716%   $209.192   $209.19   $209.20   $209.20  
  Purchase #3 $160.69   10.358%   $177.3343   $177.33   $177.35   $177.30  
  Purchase #4 $228.92   5.624%   $241.7945   $241.79   $241.80   $241.80  
  Purchase #5 $117.76   6.196%   $125.0564   $125.06   $125.05   $125.10  
  Purchase #6 $88.73   10.189%   $97.7707   $97.77   $97.75   $97.80  
  Purchase #7 $84.62   4.143%   $88.1258   $88.13   $88.15   $88.10  
  7 purchase totals = $1,098.94       $1,205.2314   $1,205.23   $1,205.25   $1,205.30