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	$77.44	12.754%	$87.3167	$87.32	$87.30	$87.30
Purchase #2	$190.56	12.561%	$214.4962	$214.50	$214.50	$214.50
Purchase #3	$36.85	10.411%	$40.6865	$40.69	$40.70	$40.70
Purchase #4	$231.40	5.498%	$244.1224	$244.12	$244.10	$244.10
Purchase #5	$234.81	3.404%	$242.8029	$242.80	$242.80	$242.80
Purchase #6	$102.83	8.750%	$111.8276	$111.83	$111.85	$111.80
Purchase #7	$57.90	5.212%	$60.9177	$60.92	$60.90	$60.90
7 purchase totals =	$931.79		$1,002.1700	$1,002.18	$1,002.15	$1,002.10