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	$134.73	7.463%	$144.7849	$144.78	$144.80	$144.80
Purchase #2	$223.41	9.356%	$244.3122	$244.31	$244.30	$244.30
Purchase #3	$183.88	3.671%	$190.6302	$190.63	$190.65	$190.60
Purchase #4	$200.51	9.275%	$219.1073	$219.11	$219.10	$219.10
Purchase #5	$127.34	10.547%	$140.7705	$140.77	$140.75	$140.80
Purchase #6	$85.81	5.449%	$90.4858	$90.49	$90.50	$90.50
Purchase #7	$115.51	9.218%	$126.1577	$126.16	$126.15	$126.20
7 purchase totals =	$1,071.19		$1,156.2486	$1,156.25	$1,156.25	$1,156.30