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	$157.40	10.819%	$174.4291	$174.43	$174.45	$174.40
Purchase #2	$100.55	5.219%	$105.7977	$105.80	$105.80	$105.80
Purchase #3	$94.30	5.624%	$99.6034	$99.60	$99.60	$99.60
Purchase #4	$188.97	11.509%	$210.7186	$210.72	$210.70	$210.70
Purchase #5	$81.84	11.806%	$91.502	$91.50	$91.50	$91.50
Purchase #6	$120.80	4.122%	$125.7794	$125.78	$125.80	$125.80
Purchase #7	$92.43	7.682%	$99.5305	$99.53	$99.55	$99.50
7 purchase totals =	$836.29		$907.3607	$907.36	$907.40	$907.30