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	$22.69	12.668%	$25.5644	$25.56	$25.55	$25.60
Purchase #2	$221.81	7.494%	$238.4324	$238.43	$238.45	$238.40
Purchase #3	$127.54	10.400%	$140.8042	$140.80	$140.80	$140.80
Purchase #4	$81.77	13.544%	$92.8449	$92.84	$92.85	$92.80
Purchase #5	$39.39	9.708%	$43.214	$43.21	$43.20	$43.20
Purchase #6	$50.41	6.586%	$53.73	$53.73	$53.75	$53.70
Purchase #7	$100.55	10.857%	$111.4667	$111.47	$111.45	$111.50
7 purchase totals =	$644.16		$706.0566	$706.04	$706.05	$706.00