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	$30.58	6.541%	$32.5802	$32.58	$32.60	$32.60
Purchase #2	$79.98	9.809%	$87.8252	$87.83	$87.85	$87.80
Purchase #3	$71.40	9.656%	$78.2944	$78.29	$78.30	$78.30
Purchase #4	$131.39	13.231%	$148.7742	$148.77	$148.75	$148.80
Purchase #5	$5.89	3.717%	$6.1089	$6.11	$6.10	$6.10
Purchase #6	$60.80	8.621%	$66.0416	$66.04	$66.05	$66.00
Purchase #7	$229.99	5.406%	$242.4233	$242.42	$242.40	$242.40
7 purchase totals =	$610.03		$662.0478	$662.04	$662.05	$662.00