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 $193.81   7.554%   $208.4504   $208.45   $208.45   $208.50  
  Purchase #2 $151.62   11.731%   $169.4065   $169.41   $169.40   $169.40  
  Purchase #3 $41.31   12.420%   $46.4407   $46.44   $46.45   $46.40  
  Purchase #4 $238.71   10.377%   $263.4809   $263.48   $263.50   $263.50  
  Purchase #5 $34.66   5.359%   $36.5174   $36.52   $36.50   $36.50  
  Purchase #6 $243.59   4.678%   $254.9851   $254.99   $255.00   $255.00  
  Purchase #7 $5.92   7.156%   $6.3436   $6.34   $6.35   $6.30  
  7 purchase totals = $909.62       $985.6246   $985.63   $985.65   $985.60