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	$137.66	4.234%	$143.4885	$143.49	$143.50	$143.50
Purchase #2	$238.64	8.144%	$258.0748	$258.07	$258.05	$258.10
Purchase #3	$43.36	4.444%	$45.2869	$45.29	$45.30	$45.30
Purchase #4	$39.32	8.267%	$42.5706	$42.57	$42.55	$42.60
Purchase #5	$144.28	8.476%	$156.5092	$156.51	$156.50	$156.50
Purchase #6	$122.95	10.464%	$135.8155	$135.82	$135.80	$135.80
Purchase #7	$137.54	11.673%	$153.595	$153.60	$153.60	$153.60
7 purchase totals =	$863.75		$935.3405	$935.35	$935.30	$935.40