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 $184.26   3.698%   $191.0739   $191.07   $191.05   $191.10  
  Purchase #2 $71.58   11.301%   $79.6693   $79.67   $79.65   $79.70  
  Purchase #3 $32.75   9.647%   $35.9094   $35.91   $35.90   $35.90  
  Purchase #4 $220.89   12.862%   $249.3009   $249.30   $249.30   $249.30  
  Purchase #5 $233.80   6.515%   $249.0321   $249.03   $249.05   $249.00  
  Purchase #6 $47.38   12.427%   $53.2679   $53.27   $53.25   $53.30  
  Purchase #7 $173.31   7.453%   $186.2268   $186.23   $186.25   $186.20  
  7 purchase totals = $963.97       $1,044.4803   $1,044.48   $1,044.45   $1,044.50