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	$48.70	8.443%	$52.8117	$52.81	$52.80	$52.80
Purchase #2	$72.93	7.213%	$78.1904	$78.19	$78.20	$78.20
Purchase #3	$112.42	5.730%	$118.8617	$118.86	$118.85	$118.90
Purchase #4	$238.79	12.232%	$267.9988	$268.00	$268.00	$268.00
Purchase #5	$88.56	3.388%	$91.5604	$91.56	$91.55	$91.60
Purchase #6	$151.64	10.468%	$167.5137	$167.51	$167.50	$167.50
Purchase #7	$145.44	6.125%	$154.3482	$154.35	$154.35	$154.30
7 purchase totals =	$858.48		$931.2849	$931.28	$931.25	$931.30