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	$114.72	4.745%	$120.1635	$120.16	$120.15	$120.20
Purchase #2	$20.98	6.624%	$22.3697	$22.37	$22.35	$22.40
Purchase #3	$17.66	13.869%	$20.1093	$20.11	$20.10	$20.10
Purchase #4	$162.78	13.265%	$184.3728	$184.37	$184.35	$184.40
Purchase #5	$151.42	13.528%	$171.9041	$171.90	$171.90	$171.90
Purchase #6	$185.51	10.673%	$205.3095	$205.31	$205.30	$205.30
Purchase #7	$17.98	11.127%	$19.9806	$19.98	$20.00	$20.00
7 purchase totals =	$671.05		$744.2095	$744.20	$744.15	$744.30