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	$30.88	5.844%	$32.6846	$32.68	$32.70	$32.70
Purchase #2	$30.88	12.218%	$34.6529	$34.65	$34.65	$34.70
Purchase #3	$164.40	13.358%	$186.3606	$186.36	$186.35	$186.40
Purchase #4	$149.46	5.235%	$157.2842	$157.28	$157.30	$157.30
Purchase #5	$234.72	4.315%	$244.8482	$244.85	$244.85	$244.80
Purchase #6	$107.25	3.604%	$111.1153	$111.12	$111.10	$111.10
Purchase #7	$53.92	11.117%	$59.9143	$59.91	$59.90	$59.90
7 purchase totals =	$771.51		$826.8601	$826.85	$826.85	$826.90