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	$39.98	5.159%	$42.0426	$42.04	$42.05	$42.00
Purchase #2	$188.74	6.230%	$200.4985	$200.50	$200.50	$200.50
Purchase #3	$235.87	11.482%	$262.9526	$262.95	$262.95	$263.00
Purchase #4	$135.50	8.315%	$146.7668	$146.77	$146.75	$146.80
Purchase #5	$42.36	7.309%	$45.4561	$45.46	$45.45	$45.50
Purchase #6	$204.65	12.183%	$229.5825	$229.58	$229.60	$229.60
Purchase #7	$131.84	9.182%	$143.9455	$143.95	$143.95	$143.90
7 purchase totals =	$978.94		$1,071.2446	$1,071.25	$1,071.25	$1,071.30