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 $234.75   13.577%   $266.622   $266.62   $266.60   $266.60  
  Purchase #2 $30.99   6.374%   $32.9653   $32.97   $32.95   $33.00  
  Purchase #3 $122.33   7.794%   $131.8644   $131.86   $131.85   $131.90  
  Purchase #4 $245.91   10.183%   $270.951   $270.95   $270.95   $271.00  
  Purchase #5 $54.45   11.519%   $60.7221   $60.72   $60.70   $60.70  
  Purchase #6 $242.74   10.510%   $268.252   $268.25   $268.25   $268.30  
  Purchase #7 $107.46   8.624%   $116.7274   $116.73   $116.75   $116.70  
  7 purchase totals = $1,038.63       $1,148.1042   $1,148.10   $1,148.05   $1,148.20