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 $241.71   10.188%   $266.3354   $266.34   $266.35   $266.30  
  Purchase #2 $69.92   9.687%   $76.6932   $76.69   $76.70   $76.70  
  Purchase #3 $35.68   5.860%   $37.7708   $37.77   $37.75   $37.80  
  Purchase #4 $210.33   3.597%   $217.8956   $217.90   $217.90   $217.90  
  Purchase #5 $165.59   10.756%   $183.4009   $183.40   $183.40   $183.40  
  Purchase #6 $178.46   10.772%   $197.6837   $197.68   $197.70   $197.70  
  Purchase #7 $41.86   8.607%   $45.4629   $45.46   $45.45   $45.50  
  7 purchase totals = $943.55       $1,025.2425   $1,025.24   $1,025.25   $1,025.30