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	$41.25	6.371%	$43.878	$43.88	$43.90	$43.90
Purchase #2	$59.36	4.531%	$62.0496	$62.05	$62.05	$62.00
Purchase #3	$207.58	12.424%	$233.3697	$233.37	$233.35	$233.40
Purchase #4	$92.73	11.741%	$103.6174	$103.62	$103.60	$103.60
Purchase #5	$99.96	11.812%	$111.7673	$111.77	$111.75	$111.80
Purchase #6	$91.37	8.519%	$99.1538	$99.15	$99.15	$99.20
Purchase #7	$244.95	5.199%	$257.685	$257.69	$257.70	$257.70
7 purchase totals =	$837.20		$911.5208	$911.53	$911.50	$911.60