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 $73.66   13.483%   $83.5916   $83.59   $83.60   $83.60  
  Purchase #2 $114.97   6.358%   $122.2798   $122.28   $122.30   $122.30  
  Purchase #3 $164.84   6.560%   $175.6535   $175.65   $175.65   $175.70  
  Purchase #4 $236.76   8.225%   $256.2335   $256.23   $256.25   $256.20  
  Purchase #5 $191.82   4.160%   $199.7997   $199.80   $199.80   $199.80  
  Purchase #6 $94.64   5.137%   $99.5017   $99.50   $99.50   $99.50  
  Purchase #7 $51.91   12.207%   $58.2467   $58.25   $58.25   $58.20  
  7 purchase totals = $928.60       $995.3065   $995.30   $995.35   $995.30