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 $232.84   7.299%   $249.835   $249.84   $249.85   $249.80  
  Purchase #2 $14.99   11.802%   $16.7591   $16.76   $16.75   $16.80  
  Purchase #3 $75.32   13.620%   $85.5786   $85.58   $85.60   $85.60  
  Purchase #4 $164.33   6.254%   $174.6072   $174.61   $174.60   $174.60  
  Purchase #5 $101.38   8.352%   $109.8473   $109.85   $109.85   $109.80  
  Purchase #6 $188.45   4.196%   $196.3574   $196.36   $196.35   $196.40  
  Purchase #7 $108.89   5.709%   $115.1065   $115.11   $115.10   $115.10  
  7 purchase totals = $886.20       $948.0911   $948.11   $948.10   $948.10