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	$12.59	4.865%	$13.2025	$13.20	$13.20	$13.20
Purchase #2	$59.70	10.788%	$66.1404	$66.14	$66.15	$66.10
Purchase #3	$13.63	11.867%	$15.2475	$15.25	$15.25	$15.20
Purchase #4	$29.50	13.580%	$33.5061	$33.51	$33.50	$33.50
Purchase #5	$122.50	12.234%	$137.4867	$137.49	$137.50	$137.50
Purchase #6	$218.27	7.113%	$233.7955	$233.80	$233.80	$233.80
Purchase #7	$90.56	4.194%	$94.3581	$94.36	$94.35	$94.40
7 purchase totals =	$546.75		$593.7368	$593.75	$593.75	$593.70