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 $239.38   9.785%   $262.8033   $262.80   $262.80   $262.80  
  Purchase #2 $238.94   7.298%   $256.3778   $256.38   $256.40   $256.40  
  Purchase #3 $91.25   6.425%   $97.1128   $97.11   $97.10   $97.10  
  Purchase #4 $86.81   13.514%   $98.5415   $98.54   $98.55   $98.50  
  Purchase #5 $25.56   13.254%   $28.9477   $28.95   $28.95   $28.90  
  Purchase #6 $211.91   10.803%   $234.8026   $234.80   $234.80   $234.80  
  Purchase #7 $66.90   4.565%   $69.954   $69.95   $69.95   $70.00  
  7 purchase totals = $960.75       $1,048.5397   $1,048.53   $1,048.55   $1,048.50