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 $137.79   6.608%   $146.8952   $146.90   $146.90   $146.90  
  Purchase #2 $158.93   10.421%   $175.4921   $175.49   $175.50   $175.50  
  Purchase #3 $208.69   13.423%   $236.7025   $236.70   $236.70   $236.70  
  Purchase #4 $56.86   6.426%   $60.5138   $60.51   $60.50   $60.50  
  Purchase #5 $186.38   4.865%   $195.4474   $195.45   $195.45   $195.40  
  Purchase #6 $204.57   8.707%   $222.3819   $222.38   $222.40   $222.40  
  Purchase #7 $42.87   11.288%   $47.7092   $47.71   $47.70   $47.70  
  7 purchase totals = $996.09       $1,085.1421   $1,085.14   $1,085.15   $1,085.10