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	$97.39	3.481%	$100.7801	$100.78	$100.80	$100.80
Purchase #2	$130.52	12.129%	$146.3508	$146.35	$146.35	$146.40
Purchase #3	$167.39	3.294%	$172.9038	$172.90	$172.90	$172.90
Purchase #4	$100.48	8.719%	$109.2409	$109.24	$109.25	$109.20
Purchase #5	$20.97	5.688%	$22.1628	$22.16	$22.15	$22.20
Purchase #6	$233.91	12.317%	$262.7207	$262.72	$262.70	$262.70
Purchase #7	$115.43	13.693%	$131.2358	$131.24	$131.25	$131.20
7 purchase totals =	$866.09		$945.3949	$945.39	$945.40	$945.40