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 $199.48   5.224%   $209.9008   $209.90   $209.90   $209.90  
  Purchase #2 $88.60   10.662%   $98.0465   $98.05   $98.05   $98.00  
  Purchase #3 $7.84   9.202%   $8.5614   $8.56   $8.55   $8.60  
  Purchase #4 $114.61   11.619%   $127.9265   $127.93   $127.95   $127.90  
  Purchase #5 $134.62   11.722%   $150.4002   $150.40   $150.40   $150.40  
  Purchase #6 $123.91   9.872%   $136.1424   $136.14   $136.15   $136.10  
  Purchase #7 $56.89   10.295%   $62.7468   $62.75   $62.75   $62.70  
  7 purchase totals = $725.95       $793.7246   $793.73   $793.75   $793.60