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 $226.89   6.823%   $242.3707   $242.37   $242.35   $242.40  
  Purchase #2 $206.62   13.600%   $234.7203   $234.72   $234.70   $234.70  
  Purchase #3 $13.37   11.739%   $14.9395   $14.94   $14.95   $14.90  
  Purchase #4 $164.85   13.775%   $187.5581   $187.56   $187.55   $187.60  
  Purchase #5 $98.66   9.131%   $107.6686   $107.67   $107.65   $107.70  
  Purchase #6 $44.90   5.707%   $47.4624   $47.46   $47.45   $47.50  
  Purchase #7 $224.31   3.635%   $232.4637   $232.46   $232.45   $232.50  
  7 purchase totals = $979.60       $1,067.1833   $1,067.18   $1,067.10   $1,067.30