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 $203.61   6.106%   $216.0424   $216.04   $216.05   $216.00  
  Purchase #2 $223.32   3.157%   $230.3702   $230.37   $230.35   $230.40  
  Purchase #3 $190.26   6.339%   $202.3206   $202.32   $202.30   $202.30  
  Purchase #4 $112.39   9.683%   $123.2727   $123.27   $123.25   $123.30  
  Purchase #5 $249.44   3.242%   $257.5268   $257.53   $257.55   $257.50  
  Purchase #6 $215.83   5.367%   $227.4136   $227.41   $227.40   $227.40  
  Purchase #7 $240.82   3.817%   $250.0121   $250.01   $250.00   $250.00  
  7 purchase totals = $1,435.67       $1,506.9584   $1,506.95   $1,506.90   $1,506.90