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 $108.51   7.172%   $116.2923   $116.29   $116.30   $116.30  
  Purchase #2 $33.54   8.456%   $36.3761   $36.38   $36.40   $36.40  
  Purchase #3 $9.54   6.223%   $10.1337   $10.13   $10.15   $10.10  
  Purchase #4 $46.74   7.331%   $50.1665   $50.17   $50.15   $50.20  
  Purchase #5 $231.91   7.115%   $248.4104   $248.41   $248.40   $248.40  
  Purchase #6 $62.92   9.472%   $68.8798   $68.88   $68.90   $68.90  
  Purchase #7 $176.40   11.217%   $196.1868   $196.19   $196.20   $196.20  
  7 purchase totals = $669.56       $726.4456   $726.45   $726.50   $726.50