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 $248.34   12.593%   $279.6135   $279.61   $279.60   $279.60  
  Purchase #2 $81.78   7.391%   $87.8244   $87.82   $87.80   $87.80  
  Purchase #3 $117.59   12.359%   $132.1229   $132.12   $132.10   $132.10  
  Purchase #4 $101.86   12.697%   $114.7932   $114.79   $114.80   $114.80  
  Purchase #5 $50.33   6.368%   $53.535   $53.54   $53.55   $53.50  
  Purchase #6 $107.26   11.545%   $119.6432   $119.64   $119.65   $119.60  
  Purchase #7 $222.52   8.736%   $241.9593   $241.96   $241.95   $242.00  
  7 purchase totals = $929.68       $1,029.4915   $1,029.48   $1,029.45   $1,029.40