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	$111.35	6.134%	$118.1802	$118.18	$118.20	$118.20
Purchase #2	$244.95	9.383%	$267.9337	$267.93	$267.95	$267.90
Purchase #3	$11.56	8.563%	$12.5499	$12.55	$12.55	$12.50
Purchase #4	$101.28	10.139%	$111.5488	$111.55	$111.55	$111.50
Purchase #5	$93.73	6.399%	$99.7278	$99.73	$99.75	$99.70
Purchase #6	$53.45	4.680%	$55.9515	$55.95	$55.95	$56.00
Purchase #7	$71.71	12.322%	$80.5461	$80.55	$80.55	$80.50
7 purchase totals =	$688.03		$746.4380	$746.44	$746.50	$746.30