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 $83.47   13.773%   $94.9663   $94.97   $94.95   $95.00  
  Purchase #2 $18.83   3.599%   $19.5077   $19.51   $19.50   $19.50  
  Purchase #3 $151.76   11.749%   $169.5903   $169.59   $169.60   $169.60  
  Purchase #4 $155.39   4.102%   $161.7641   $161.76   $161.75   $161.80  
  Purchase #5 $106.82   6.369%   $113.6234   $113.62   $113.60   $113.60  
  Purchase #6 $140.83   6.432%   $149.8882   $149.89   $149.90   $149.90  
  Purchase #7 $61.85   12.673%   $69.6883   $69.69   $69.70   $69.70  
  7 purchase totals = $718.95       $779.0283   $779.03   $779.00   $779.10