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 $201.34   12.621%   $226.7511   $226.75   $226.75   $226.80  
  Purchase #2 $191.38   10.238%   $210.9735   $210.97   $210.95   $211.00  
  Purchase #3 $157.95   13.232%   $178.8499   $178.85   $178.85   $178.80  
  Purchase #4 $249.72   8.578%   $271.141   $271.14   $271.15   $271.10  
  Purchase #5 $21.38   13.380%   $24.2406   $24.24   $24.25   $24.20  
  Purchase #6 $62.68   6.485%   $66.7448   $66.74   $66.75   $66.70  
  Purchase #7 $198.43   9.572%   $217.4237   $217.42   $217.40   $217.40  
  7 purchase totals = $1,082.88       $1,196.1246   $1,196.11   $1,196.10   $1,196.00