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 $241.57   11.192%   $268.6065   $268.61   $268.60   $268.60  
  Purchase #2 $136.58   8.322%   $147.9462   $147.95   $147.95   $147.90  
  Purchase #3 $151.31   12.831%   $170.7246   $170.72   $170.70   $170.70  
  Purchase #4 $188.76   6.738%   $201.4786   $201.48   $201.50   $201.50  
  Purchase #5 $32.94   10.516%   $36.404   $36.40   $36.40   $36.40  
  Purchase #6 $205.62   3.707%   $213.2423   $213.24   $213.25   $213.20  
  Purchase #7 $78.79   12.474%   $88.6183   $88.62   $88.60   $88.60  
  7 purchase totals = $1,035.57       $1,127.0205   $1,127.02   $1,127.00   $1,126.90