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 $234.99   6.226%   $249.6205   $249.62   $249.60   $249.60  
  Purchase #2 $171.90   5.170%   $180.7872   $180.79   $180.80   $180.80  
  Purchase #3 $55.42   3.263%   $57.2284   $57.23   $57.25   $57.20  
  Purchase #4 $129.84   5.119%   $136.4865   $136.49   $136.50   $136.50  
  Purchase #5 $184.46   6.309%   $196.0976   $196.10   $196.10   $196.10  
  Purchase #6 $60.80   6.515%   $64.7611   $64.76   $64.75   $64.80  
  Purchase #7 $114.49   10.263%   $126.2401   $126.24   $126.25   $126.20  
  7 purchase totals = $951.90       $1,011.2214   $1,011.23   $1,011.25   $1,011.20