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	$90.63	10.416%	$100.07	$100.07	$100.05	$100.10
Purchase #2	$35.26	12.301%	$39.5973	$39.60	$39.60	$39.60
Purchase #3	$158.68	8.338%	$171.9107	$171.91	$171.90	$171.90
Purchase #4	$114.59	9.852%	$125.8794	$125.88	$125.90	$125.90
Purchase #5	$144.29	10.504%	$159.4462	$159.45	$159.45	$159.40
Purchase #6	$135.66	11.814%	$151.6869	$151.69	$151.70	$151.70
Purchase #7	$162.78	11.456%	$181.4281	$181.43	$181.45	$181.40
7 purchase totals =	$841.89		$930.0186	$930.03	$930.05	$930.00