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	$230.44	11.141%	$256.1133	$256.11	$256.10	$256.10
Purchase #2	$234.41	4.273%	$244.4263	$244.43	$244.45	$244.40
Purchase #3	$173.90	3.428%	$179.8613	$179.86	$179.85	$179.90
Purchase #4	$189.29	11.361%	$210.7952	$210.80	$210.80	$210.80
Purchase #5	$79.99	13.389%	$90.6999	$90.70	$90.70	$90.70
Purchase #6	$67.91	3.412%	$70.2271	$70.23	$70.25	$70.20
Purchase #7	$96.63	7.133%	$103.5226	$103.52	$103.50	$103.50
7 purchase totals =	$1,072.57		$1,155.6457	$1,155.65	$1,155.65	$1,155.60