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 $227.95   13.614%   $258.9831   $258.98   $259.00   $259.00  
  Purchase #2 $199.59   5.707%   $210.9806   $210.98   $211.00   $211.00  
  Purchase #3 $86.44   9.721%   $94.8428   $94.84   $94.85   $94.80  
  Purchase #4 $64.30   3.608%   $66.6199   $66.62   $66.60   $66.60  
  Purchase #5 $91.45   11.506%   $101.9722   $101.97   $101.95   $102.00  
  Purchase #6 $102.98   4.190%   $107.2949   $107.29   $107.30   $107.30  
  Purchase #7 $239.28   9.779%   $262.6792   $262.68   $262.70   $262.70  
  7 purchase totals = $1,011.99       $1,103.3727   $1,103.36   $1,103.40   $1,103.40