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 $116.97   6.669%   $124.7707   $124.77   $124.75   $124.80  
  Purchase #2 $224.28   4.187%   $233.6706   $233.67   $233.65   $233.70  
  Purchase #3 $157.56   7.497%   $169.3723   $169.37   $169.35   $169.40  
  Purchase #4 $201.39   4.718%   $210.8916   $210.89   $210.90   $210.90  
  Purchase #5 $45.69   11.817%   $51.0892   $51.09   $51.10   $51.10  
  Purchase #6 $172.42   11.872%   $192.8897   $192.89   $192.90   $192.90  
  Purchase #7 $51.50   3.737%   $53.4246   $53.42   $53.40   $53.40  
  7 purchase totals = $969.81       $1,036.1087   $1,036.10   $1,036.05   $1,036.20