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	$70.87	13.312%	$80.3042	$80.30	$80.30	$80.30
Purchase #2	$160.39	3.612%	$166.1833	$166.18	$166.20	$166.20
Purchase #3	$52.68	12.204%	$59.1091	$59.11	$59.10	$59.10
Purchase #4	$40.50	3.187%	$41.7907	$41.79	$41.80	$41.80
Purchase #5	$245.72	3.462%	$254.2268	$254.23	$254.25	$254.20
Purchase #6	$117.41	11.278%	$130.6515	$130.65	$130.65	$130.70
Purchase #7	$13.29	3.722%	$13.7847	$13.78	$13.80	$13.80
7 purchase totals =	$700.86		$746.0503	$746.04	$746.10	$746.10