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 $60.51   13.217%   $68.5076   $68.51   $68.50   $68.50  
  Purchase #2 $249.75   7.493%   $268.4638   $268.46   $268.45   $268.50  
  Purchase #3 $161.35   4.160%   $168.0622   $168.06   $168.05   $168.10  
  Purchase #4 $25.49   8.543%   $27.6676   $27.67   $27.65   $27.70  
  Purchase #5 $151.82   11.585%   $169.4083   $169.41   $169.40   $169.40  
  Purchase #6 $102.84   13.185%   $116.3995   $116.40   $116.40   $116.40  
  Purchase #7 $126.77   5.405%   $133.6219   $133.62   $133.60   $133.60  
  7 purchase totals = $878.53       $952.1309   $952.13   $952.05   $952.20