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 $244.42   13.576%   $277.6025   $277.60   $277.60   $277.60  
  Purchase #2 $240.29   12.505%   $270.3383   $270.34   $270.35   $270.30  
  Purchase #3 $109.73   4.710%   $114.8983   $114.90   $114.90   $114.90  
  Purchase #4 $182.64   12.637%   $205.7202   $205.72   $205.70   $205.70  
  Purchase #5 $54.71   10.736%   $60.5837   $60.58   $60.60   $60.60  
  Purchase #6 $229.66   5.716%   $242.7874   $242.79   $242.80   $242.80  
  Purchase #7 $24.38   11.586%   $27.2047   $27.20   $27.20   $27.20  
  7 purchase totals = $1,085.83       $1,199.1351   $1,199.13   $1,199.15   $1,199.10