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	$96.82	3.741%	$100.442	$100.44	$100.45	$100.40
Purchase #2	$127.90	8.595%	$138.893	$138.89	$138.90	$138.90
Purchase #3	$146.75	7.306%	$157.4716	$157.47	$157.45	$157.50
Purchase #4	$47.38	12.701%	$53.3977	$53.40	$53.40	$53.40
Purchase #5	$151.64	8.242%	$164.1382	$164.14	$164.15	$164.10
Purchase #6	$57.29	3.110%	$59.0717	$59.07	$59.05	$59.10
Purchase #7	$210.73	13.133%	$238.4052	$238.41	$238.40	$238.40
7 purchase totals =	$838.51		$911.8194	$911.82	$911.80	$911.80