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 $55.51   11.562%   $61.9281   $61.93   $61.95   $61.90  
  Purchase #2 $194.47   3.635%   $201.539   $201.54   $201.55   $201.50  
  Purchase #3 $5.89   10.240%   $6.4931   $6.49   $6.50   $6.50  
  Purchase #4 $139.54   6.412%   $148.4873   $148.49   $148.50   $148.50  
  Purchase #5 $65.61   4.483%   $68.5513   $68.55   $68.55   $68.60  
  Purchase #6 $213.76   6.204%   $227.0217   $227.02   $227.00   $227.00  
  Purchase #7 $114.94   7.209%   $123.226   $123.23   $123.25   $123.20  
  7 purchase totals = $789.72       $837.2465   $837.25   $837.30   $837.20