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 $224.54   12.230%   $252.0012   $252.00   $252.00   $252.00  
  Purchase #2 $44.83   9.344%   $49.0189   $49.02   $49.00   $49.00  
  Purchase #3 $188.93   9.536%   $206.9464   $206.95   $206.95   $206.90  
  Purchase #4 $229.69   4.229%   $239.4036   $239.40   $239.40   $239.40  
  Purchase #5 $185.54   7.476%   $199.411   $199.41   $199.40   $199.40  
  Purchase #6 $56.50   6.688%   $60.2787   $60.28   $60.30   $60.30  
  Purchase #7 $205.99   3.138%   $212.454   $212.45   $212.45   $212.50  
  7 purchase totals = $1,136.02       $1,219.5138   $1,219.51   $1,219.50   $1,219.50