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 $119.39   7.187%   $127.9706   $127.97   $127.95   $128.00  
  Purchase #2 $23.91   3.103%   $24.6519   $24.65   $24.65   $24.70  
  Purchase #3 $159.67   5.854%   $169.0171   $169.02   $169.00   $169.00  
  Purchase #4 $55.32   13.586%   $62.8358   $62.84   $62.85   $62.80  
  Purchase #5 $86.96   8.873%   $94.676   $94.68   $94.70   $94.70  
  Purchase #6 $91.56   5.382%   $96.4878   $96.49   $96.50   $96.50  
  Purchase #7 $180.99   4.657%   $189.4187   $189.42   $189.40   $189.40  
  7 purchase totals = $717.80       $765.0579   $765.07   $765.05   $765.10