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	$85.64	4.627%	$89.6026	$89.60	$89.60	$89.60
Purchase #2	$143.77	12.765%	$162.1222	$162.12	$162.10	$162.10
Purchase #3	$83.50	9.563%	$91.4851	$91.49	$91.50	$91.50
Purchase #4	$220.63	4.539%	$230.6444	$230.64	$230.65	$230.60
Purchase #5	$231.65	9.492%	$253.6382	$253.64	$253.65	$253.60
Purchase #6	$246.71	3.505%	$255.3572	$255.36	$255.35	$255.40
Purchase #7	$130.93	11.732%	$146.2907	$146.29	$146.30	$146.30
7 purchase totals =	$1,142.83		$1,229.1404	$1,229.14	$1,229.15	$1,229.10