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 $215.95   13.767%   $245.6798   $245.68   $245.70   $245.70  
  Purchase #2 $148.87   6.147%   $158.021   $158.02   $158.00   $158.00  
  Purchase #3 $140.74   9.259%   $153.7711   $153.77   $153.75   $153.80  
  Purchase #4 $147.89   13.373%   $167.6673   $167.67   $167.65   $167.70  
  Purchase #5 $114.50   6.423%   $121.8543   $121.85   $121.85   $121.90  
  Purchase #6 $123.63   3.622%   $128.1079   $128.11   $128.10   $128.10  
  Purchase #7 $224.91   7.422%   $241.6028   $241.60   $241.60   $241.60  
  7 purchase totals = $1,116.49       $1,216.7042   $1,216.70   $1,216.65   $1,216.80