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 $237.71   6.403%   $252.9306   $252.93   $252.95   $252.90  
  Purchase #2 $214.30   6.275%   $227.7473   $227.75   $227.75   $227.70  
  Purchase #3 $87.59   9.496%   $95.9075   $95.91   $95.90   $95.90  
  Purchase #4 $49.58   10.134%   $54.6044   $54.60   $54.60   $54.60  
  Purchase #5 $67.93   3.513%   $70.3164   $70.32   $70.30   $70.30  
  Purchase #6 $132.89   3.405%   $137.4149   $137.41   $137.40   $137.40  
  Purchase #7 $176.91   13.809%   $201.3395   $201.34   $201.35   $201.30  
  7 purchase totals = $966.91       $1,040.2606   $1,040.26   $1,040.25   $1,040.10