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	$123.77	7.340%	$132.8547	$132.85	$132.85	$132.90
Purchase #2	$117.64	11.170%	$130.7804	$130.78	$130.80	$130.80
Purchase #3	$84.62	6.583%	$90.1905	$90.19	$90.20	$90.20
Purchase #4	$45.86	7.174%	$49.15	$49.15	$49.15	$49.20
Purchase #5	$173.35	8.730%	$188.4835	$188.48	$188.50	$188.50
Purchase #6	$81.55	12.402%	$91.6638	$91.66	$91.65	$91.70
Purchase #7	$115.50	10.479%	$127.6032	$127.60	$127.60	$127.60
7 purchase totals =	$742.29		$810.7261	$810.71	$810.75	$810.90