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	$129.38	4.427%	$135.1077	$135.11	$135.10	$135.10
Purchase #2	$35.76	5.385%	$37.6857	$37.69	$37.70	$37.70
Purchase #3	$175.55	3.612%	$181.8909	$181.89	$181.90	$181.90
Purchase #4	$197.83	13.200%	$223.9436	$223.94	$223.95	$223.90
Purchase #5	$85.48	10.388%	$94.3597	$94.36	$94.35	$94.40
Purchase #6	$178.48	5.621%	$188.5124	$188.51	$188.50	$188.50
Purchase #7	$52.62	12.425%	$59.158	$59.16	$59.15	$59.20
7 purchase totals =	$855.10		$920.6580	$920.66	$920.65	$920.70