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	$235.85	8.333%	$255.5034	$255.50	$255.50	$255.50
Purchase #2	$37.78	10.347%	$41.6891	$41.69	$41.70	$41.70
Purchase #3	$150.50	3.236%	$155.3702	$155.37	$155.35	$155.40
Purchase #4	$18.56	6.113%	$19.6946	$19.69	$19.70	$19.70
Purchase #5	$6.96	9.200%	$7.6003	$7.60	$7.60	$7.60
Purchase #6	$17.76	3.223%	$18.3324	$18.33	$18.35	$18.30
Purchase #7	$130.30	12.144%	$146.1236	$146.12	$146.10	$146.10
7 purchase totals =	$597.71		$644.3136	$644.30	$644.30	$644.30