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	$9.95	4.647%	$10.4124	$10.41	$10.40	$10.40
Purchase #2	$186.68	5.781%	$197.472	$197.47	$197.45	$197.50
Purchase #3	$55.76	6.819%	$59.5623	$59.56	$59.55	$59.60
Purchase #4	$59.97	13.420%	$68.018	$68.02	$68.00	$68.00
Purchase #5	$98.64	5.320%	$103.8876	$103.89	$103.90	$103.90
Purchase #6	$99.41	9.362%	$108.7168	$108.72	$108.70	$108.70
Purchase #7	$249.71	10.153%	$275.0631	$275.06	$275.05	$275.10
7 purchase totals =	$760.12		$823.1322	$823.13	$823.05	$823.20