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	$159.41	3.828%	$165.5122	$165.51	$165.50	$165.50
Purchase #2	$93.29	9.278%	$101.9454	$101.95	$101.95	$101.90
Purchase #3	$59.66	4.164%	$62.1442	$62.14	$62.15	$62.10
Purchase #4	$75.27	12.703%	$84.8315	$84.83	$84.85	$84.80
Purchase #5	$18.74	9.378%	$20.4974	$20.50	$20.50	$20.50
Purchase #6	$90.83	5.609%	$95.9247	$95.92	$95.90	$95.90
Purchase #7	$111.48	11.180%	$123.9435	$123.94	$123.95	$123.90
7 purchase totals =	$608.68		$654.7989	$654.79	$654.80	$654.60