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 $164.27   12.154%   $184.2354   $184.24   $184.25   $184.20  
  Purchase #2 $37.70   10.585%   $41.6905   $41.69   $41.70   $41.70  
  Purchase #3 $66.76   12.514%   $75.1143   $75.11   $75.10   $75.10  
  Purchase #4 $81.49   3.731%   $84.5304   $84.53   $84.55   $84.50  
  Purchase #5 $14.62   6.374%   $15.5519   $15.55   $15.55   $15.60  
  Purchase #6 $189.92   8.627%   $206.3044   $206.30   $206.30   $206.30  
  Purchase #7 $249.59   6.392%   $265.5438   $265.54   $265.55   $265.50  
  7 purchase totals = $804.35       $872.9707   $872.96   $873.00   $872.90