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	$212.66	3.378%	$219.8437	$219.84	$219.85	$219.80
Purchase #2	$153.71	12.272%	$172.5733	$172.57	$172.55	$172.60
Purchase #3	$48.32	13.411%	$54.8002	$54.80	$54.80	$54.80
Purchase #4	$176.69	4.453%	$184.558	$184.56	$184.55	$184.60
Purchase #5	$172.89	10.199%	$190.5231	$190.52	$190.50	$190.50
Purchase #6	$173.76	11.343%	$193.4696	$193.47	$193.45	$193.50
Purchase #7	$232.41	13.794%	$264.4686	$264.47	$264.45	$264.50
7 purchase totals =	$1,170.44		$1,280.2365	$1,280.23	$1,280.15	$1,280.30