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	$233.93	6.210%	$248.4571	$248.46	$248.45	$248.50
Purchase #2	$234.64	3.186%	$242.1156	$242.12	$242.10	$242.10
Purchase #3	$82.67	8.687%	$89.8515	$89.85	$89.85	$89.90
Purchase #4	$116.29	9.742%	$127.619	$127.62	$127.60	$127.60
Purchase #5	$147.34	5.368%	$155.2492	$155.25	$155.25	$155.20
Purchase #6	$10.59	10.131%	$11.6629	$11.66	$11.65	$11.70
Purchase #7	$100.91	7.174%	$108.1493	$108.15	$108.15	$108.10
7 purchase totals =	$926.37		$983.1046	$983.11	$983.05	$983.10