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 $232.69   6.764%   $248.4292   $248.43   $248.45   $248.40  
  Purchase #2 $165.33   11.236%   $183.9065   $183.91   $183.90   $183.90  
  Purchase #3 $89.88   7.741%   $96.8376   $96.84   $96.85   $96.80  
  Purchase #4 $102.42   4.730%   $107.2645   $107.26   $107.25   $107.30  
  Purchase #5 $125.89   9.548%   $137.91   $137.91   $137.90   $137.90  
  Purchase #6 $60.45   7.310%   $64.8689   $64.87   $64.85   $64.90  
  Purchase #7 $165.59   11.105%   $183.9788   $183.98   $184.00   $184.00  
  7 purchase totals = $942.25       $1,023.1955   $1,023.20   $1,023.20   $1,023.20