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	$62.31	6.685%	$66.4754	$66.48	$66.50	$66.50
Purchase #2	$179.58	7.213%	$192.5331	$192.53	$192.55	$192.50
Purchase #3	$201.85	9.586%	$221.1993	$221.20	$221.20	$221.20
Purchase #4	$32.66	13.702%	$37.1351	$37.14	$37.15	$37.10
Purchase #5	$19.40	4.685%	$20.3089	$20.31	$20.30	$20.30
Purchase #6	$10.29	11.466%	$11.4699	$11.47	$11.45	$11.50
Purchase #7	$93.72	9.616%	$102.7321	$102.73	$102.75	$102.70
7 purchase totals =	$599.81		$651.8538	$651.86	$651.90	$651.80