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 $93.31   6.763%   $99.6206   $99.62   $99.60   $99.60  
  Purchase #2 $224.51   8.713%   $244.0716   $244.07   $244.05   $244.10  
  Purchase #3 $53.63   7.440%   $57.6201   $57.62   $57.60   $57.60  
  Purchase #4 $175.37   12.543%   $197.3667   $197.37   $197.35   $197.40  
  Purchase #5 $127.29   4.482%   $132.9951   $133.00   $133.00   $133.00  
  Purchase #6 $92.71   12.786%   $104.5639   $104.56   $104.55   $104.60  
  Purchase #7 $249.54   11.349%   $277.8603   $277.86   $277.85   $277.90  
  7 purchase totals = $1,016.36       $1,114.0983   $1,114.10   $1,114.00   $1,114.20