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 $176.53   12.869%   $199.2476   $199.25   $199.25   $199.20  
  Purchase #2 $29.71   10.271%   $32.7615   $32.76   $32.75   $32.80  
  Purchase #3 $30.54   13.176%   $34.564   $34.56   $34.55   $34.60  
  Purchase #4 $209.25   4.561%   $218.7939   $218.79   $218.80   $218.80  
  Purchase #5 $77.43   12.510%   $87.1165   $87.12   $87.10   $87.10  
  Purchase #6 $205.93   10.511%   $227.5753   $227.58   $227.60   $227.60  
  Purchase #7 $216.84   10.773%   $240.2002   $240.20   $240.20   $240.20  
  7 purchase totals = $946.23       $1,040.2590   $1,040.26   $1,040.25   $1,040.30