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	$110.99	11.198%	$123.4187	$123.42	$123.40	$123.40
Purchase #2	$85.87	10.541%	$94.9216	$94.92	$94.90	$94.90
Purchase #3	$99.43	12.399%	$111.7583	$111.76	$111.75	$111.80
Purchase #4	$235.35	5.760%	$248.9062	$248.91	$248.90	$248.90
Purchase #5	$41.78	8.582%	$45.3656	$45.37	$45.35	$45.40
Purchase #6	$141.64	9.254%	$154.7474	$154.75	$154.75	$154.70
Purchase #7	$53.51	12.675%	$60.2924	$60.29	$60.30	$60.30
7 purchase totals =	$768.57		$839.4102	$839.42	$839.35	$839.40