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 $44.73   11.598%   $49.9178   $49.92   $49.90   $49.90  
  Purchase #2 $240.84   12.568%   $271.1088   $271.11   $271.10   $271.10  
  Purchase #3 $69.72   7.652%   $75.055   $75.06   $75.05   $75.10  
  Purchase #4 $107.69   4.674%   $112.7234   $112.72   $112.70   $112.70  
  Purchase #5 $239.37   9.485%   $262.0742   $262.07   $262.05   $262.10  
  Purchase #6 $61.93   7.144%   $66.3543   $66.35   $66.35   $66.40  
  Purchase #7 $51.95   13.634%   $59.0329   $59.03   $59.05   $59.00  
  7 purchase totals = $816.23       $896.2664   $896.26   $896.20   $896.30