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 $218.34   13.542%   $247.9076   $247.91   $247.90   $247.90  
  Purchase #2 $201.99   12.579%   $227.3983   $227.40   $227.40   $227.40  
  Purchase #3 $215.27   8.489%   $233.5443   $233.54   $233.55   $233.50  
  Purchase #4 $15.91   11.810%   $17.789   $17.79   $17.80   $17.80  
  Purchase #5 $193.86   6.434%   $206.333   $206.33   $206.35   $206.30  
  Purchase #6 $109.45   5.519%   $115.4905   $115.49   $115.50   $115.50  
  Purchase #7 $220.41   5.684%   $232.9381   $232.94   $232.95   $232.90  
  7 purchase totals = $1,175.23       $1,281.4008   $1,281.40   $1,281.45   $1,281.30