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	$25.52	7.769%	$27.5026	$27.50	$27.50	$27.50
Purchase #2	$169.71	4.595%	$177.5082	$177.51	$177.50	$177.50
Purchase #3	$53.39	12.258%	$59.9345	$59.93	$59.95	$59.90
Purchase #4	$155.43	11.223%	$172.8739	$172.87	$172.85	$172.90
Purchase #5	$22.48	10.239%	$24.7817	$24.78	$24.80	$24.80
Purchase #6	$62.31	8.731%	$67.7503	$67.75	$67.75	$67.80
Purchase #7	$13.29	9.307%	$14.5269	$14.53	$14.55	$14.50
7 purchase totals =	$502.13		$544.8781	$544.87	$544.90	$544.90