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 $236.71   5.721%   $250.2522   $250.25   $250.25   $250.30  
  Purchase #2 $234.99   7.818%   $253.3615   $253.36   $253.35   $253.40  
  Purchase #3 $83.50   5.869%   $88.4006   $88.40   $88.40   $88.40  
  Purchase #4 $183.49   8.368%   $198.8444   $198.84   $198.85   $198.80  
  Purchase #5 $166.38   5.505%   $175.5392   $175.54   $175.55   $175.50  
  Purchase #6 $54.97   8.739%   $59.7738   $59.77   $59.75   $59.80  
  Purchase #7 $17.79   4.206%   $18.5382   $18.54   $18.55   $18.50  
  7 purchase totals = $977.83       $1,044.7099   $1,044.70   $1,044.70   $1,044.70