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	$242.64	13.549%	$275.5153	$275.52	$275.50	$275.50
Purchase #2	$84.79	7.312%	$90.9898	$90.99	$91.00	$91.00
Purchase #3	$100.69	13.675%	$114.4594	$114.46	$114.45	$114.50
Purchase #4	$47.95	3.551%	$49.6527	$49.65	$49.65	$49.70
Purchase #5	$157.75	9.258%	$172.3545	$172.35	$172.35	$172.40
Purchase #6	$41.77	4.166%	$43.5101	$43.51	$43.50	$43.50
Purchase #7	$247.44	10.640%	$273.7676	$273.77	$273.75	$273.80
7 purchase totals =	$923.03		$1,020.2494	$1,020.25	$1,020.20	$1,020.40