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 $63.36   10.356%   $69.9216   $69.92   $69.90   $69.90  
  Purchase #2 $249.46   5.836%   $264.0185   $264.02   $264.00   $264.00  
  Purchase #3 $210.98   3.741%   $218.8728   $218.87   $218.85   $218.90  
  Purchase #4 $161.40   4.249%   $168.2579   $168.26   $168.25   $168.30  
  Purchase #5 $112.90   7.672%   $121.5617   $121.56   $121.55   $121.60  
  Purchase #6 $232.98   7.395%   $250.2089   $250.21   $250.20   $250.20  
  Purchase #7 $151.90   3.455%   $157.1481   $157.15   $157.15   $157.10  
  7 purchase totals = $1,182.98       $1,249.9895   $1,249.99   $1,249.90   $1,250.00