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 $245.70   12.497%   $276.4051   $276.41   $276.40   $276.40  
  Purchase #2 $239.29   3.198%   $246.9425   $246.94   $246.95   $246.90  
  Purchase #3 $114.76   5.637%   $121.229   $121.23   $121.25   $121.20  
  Purchase #4 $60.37   8.784%   $65.6729   $65.67   $65.65   $65.70  
  Purchase #5 $193.72   10.602%   $214.2582   $214.26   $214.25   $214.30  
  Purchase #6 $126.97   4.864%   $133.1458   $133.15   $133.15   $133.10  
  Purchase #7 $108.78   6.648%   $116.0117   $116.01   $116.00   $116.00  
  7 purchase totals = $1,089.59       $1,173.6652   $1,173.67   $1,173.65   $1,173.60