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 $214.80   11.621%   $239.7619   $239.76   $239.75   $239.80  
  Purchase #2 $140.74   9.276%   $153.795   $153.80   $153.80   $153.80  
  Purchase #3 $229.69   10.240%   $253.2103   $253.21   $253.20   $253.20  
  Purchase #4 $228.74   3.301%   $236.2907   $236.29   $236.30   $236.30  
  Purchase #5 $95.30   13.228%   $107.9063   $107.91   $107.90   $107.90  
  Purchase #6 $79.85   12.556%   $89.876   $89.88   $89.90   $89.90  
  Purchase #7 $72.43   10.747%   $80.2141   $80.21   $80.20   $80.20  
  7 purchase totals = $1,061.55       $1,161.0543   $1,161.06   $1,161.05   $1,161.10