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 $233.97   10.271%   $258.0011   $258.00   $258.00   $258.00  
  Purchase #2 $170.57   3.565%   $176.6508   $176.65   $176.65   $176.70  
  Purchase #3 $245.38   5.598%   $259.1164   $259.12   $259.10   $259.10  
  Purchase #4 $14.60   10.696%   $16.1616   $16.16   $16.15   $16.20  
  Purchase #5 $159.78   4.507%   $166.9813   $166.98   $167.00   $167.00  
  Purchase #6 $242.63   8.576%   $263.4379   $263.44   $263.45   $263.40  
  Purchase #7 $180.84   8.372%   $195.9799   $195.98   $196.00   $196.00  
  7 purchase totals = $1,247.77       $1,336.3290   $1,336.33   $1,336.35   $1,336.40