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	$165.95	5.210%	$174.596	$174.60	$174.60	$174.60
Purchase #2	$191.84	4.574%	$200.6148	$200.61	$200.60	$200.60
Purchase #3	$84.40	8.338%	$91.4373	$91.44	$91.45	$91.40
Purchase #4	$124.32	11.505%	$138.623	$138.62	$138.60	$138.60
Purchase #5	$244.64	4.344%	$255.2672	$255.27	$255.25	$255.30
Purchase #6	$19.31	8.635%	$20.9774	$20.98	$21.00	$21.00
Purchase #7	$91.64	5.484%	$96.6655	$96.67	$96.65	$96.70
7 purchase totals =	$922.10		$978.1812	$978.19	$978.15	$978.20