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 $223.55   13.141%   $252.9267   $252.93   $252.95   $252.90  
  Purchase #2 $216.63   11.852%   $242.305   $242.31   $242.30   $242.30  
  Purchase #3 $67.29   9.457%   $73.6536   $73.65   $73.65   $73.70  
  Purchase #4 $127.42   4.493%   $133.145   $133.15   $133.15   $133.10  
  Purchase #5 $156.94   11.333%   $174.726   $174.73   $174.75   $174.70  
  Purchase #6 $132.32   12.342%   $148.6509   $148.65   $148.65   $148.70  
  Purchase #7 $211.81   7.526%   $227.7508   $227.75   $227.75   $227.80  
  7 purchase totals = $1,135.96       $1,253.1580   $1,253.17   $1,253.20   $1,253.20