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	$99.45	4.324%	$103.7502	$103.75	$103.75	$103.80
Purchase #2	$172.42	9.399%	$188.6258	$188.63	$188.65	$188.60
Purchase #3	$147.70	11.549%	$164.7579	$164.76	$164.75	$164.80
Purchase #4	$103.47	7.304%	$111.0274	$111.03	$111.05	$111.00
Purchase #5	$48.53	7.474%	$52.1571	$52.16	$52.15	$52.20
Purchase #6	$32.77	4.520%	$34.2512	$34.25	$34.25	$34.30
Purchase #7	$20.54	9.295%	$22.4492	$22.45	$22.45	$22.40
7 purchase totals =	$624.88		$677.0188	$677.03	$677.05	$677.10