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	$130.54	10.847%	$144.6997	$144.70	$144.70	$144.70
Purchase #2	$96.82	3.370%	$100.0828	$100.08	$100.10	$100.10
Purchase #3	$228.81	11.257%	$254.5671	$254.57	$254.55	$254.60
Purchase #4	$42.56	13.512%	$48.3107	$48.31	$48.30	$48.30
Purchase #5	$27.39	6.484%	$29.166	$29.17	$29.15	$29.20
Purchase #6	$145.93	4.435%	$152.402	$152.40	$152.40	$152.40
Purchase #7	$241.49	13.638%	$274.4244	$274.42	$274.40	$274.40
7 purchase totals =	$913.54		$1,003.6527	$1,003.65	$1,003.60	$1,003.70