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 $228.78   5.574%   $241.5322   $241.53   $241.55   $241.50  
  Purchase #2 $106.30   7.656%   $114.4383   $114.44   $114.45   $114.40  
  Purchase #3 $86.93   12.146%   $97.4885   $97.49   $97.50   $97.50  
  Purchase #4 $240.63   3.381%   $248.7657   $248.77   $248.75   $248.80  
  Purchase #5 $76.56   11.798%   $85.5925   $85.59   $85.60   $85.60  
  Purchase #6 $37.31   6.248%   $39.6411   $39.64   $39.65   $39.60  
  Purchase #7 $54.92   9.569%   $60.1753   $60.18   $60.20   $60.20  
  7 purchase totals = $831.43       $887.6336   $887.64   $887.70   $887.60