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 $62.55   6.604%   $66.6808   $66.68   $66.70   $66.70  
  Purchase #2 $180.33   3.693%   $186.9896   $186.99   $187.00   $187.00  
  Purchase #3 $111.26   4.865%   $116.6728   $116.67   $116.65   $116.70  
  Purchase #4 $154.53   13.687%   $175.6805   $175.68   $175.70   $175.70  
  Purchase #5 $71.32   7.866%   $76.93   $76.93   $76.95   $76.90  
  Purchase #6 $42.88   9.833%   $47.0964   $47.10   $47.10   $47.10  
  Purchase #7 $137.97   7.586%   $148.4364   $148.44   $148.45   $148.40  
  7 purchase totals = $760.84       $818.4865   $818.49   $818.55   $818.50