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	$142.37	3.337%	$147.1209	$147.12	$147.10	$147.10
Purchase #2	$42.57	7.677%	$45.8381	$45.84	$45.85	$45.80
Purchase #3	$146.42	12.374%	$164.538	$164.54	$164.55	$164.50
Purchase #4	$70.64	11.124%	$78.498	$78.50	$78.50	$78.50
Purchase #5	$105.74	5.174%	$111.211	$111.21	$111.20	$111.20
Purchase #6	$54.87	3.607%	$56.8492	$56.85	$56.85	$56.80
Purchase #7	$22.32	4.693%	$23.3675	$23.37	$23.35	$23.40
7 purchase totals =	$584.93		$627.4227	$627.43	$627.40	$627.30