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 $110.92   3.557%   $114.8654   $114.87   $114.85   $114.90  
  Purchase #2 $29.73   6.702%   $31.7225   $31.72   $31.70   $31.70  
  Purchase #3 $242.30   9.367%   $264.9962   $265.00   $265.00   $265.00  
  Purchase #4 $105.45   10.732%   $116.7669   $116.77   $116.75   $116.80  
  Purchase #5 $115.33   3.531%   $119.4023   $119.40   $119.40   $119.40  
  Purchase #6 $125.73   11.282%   $139.9149   $139.91   $139.90   $139.90  
  Purchase #7 $200.26   12.730%   $225.7531   $225.75   $225.75   $225.80  
  7 purchase totals = $929.72       $1,013.4213   $1,013.42   $1,013.35   $1,013.50