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	$9.88	6.386%	$10.5109	$10.51	$10.50	$10.50
Purchase #2	$157.84	6.349%	$167.8613	$167.86	$167.85	$167.90
Purchase #3	$237.26	11.657%	$264.9174	$264.92	$264.90	$264.90
Purchase #4	$117.64	8.188%	$127.2724	$127.27	$127.25	$127.30
Purchase #5	$73.30	9.302%	$80.1184	$80.12	$80.10	$80.10
Purchase #6	$181.26	10.389%	$200.0911	$200.09	$200.10	$200.10
Purchase #7	$124.76	11.450%	$139.045	$139.05	$139.05	$139.00
7 purchase totals =	$901.94		$989.8165	$989.82	$989.75	$989.80