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	$52.56	6.123%	$55.7782	$55.78	$55.80	$55.80
Purchase #2	$149.40	13.836%	$170.071	$170.07	$170.05	$170.10
Purchase #3	$18.62	12.108%	$20.8745	$20.87	$20.85	$20.90
Purchase #4	$118.63	4.300%	$123.7311	$123.73	$123.75	$123.70
Purchase #5	$152.68	8.544%	$165.725	$165.73	$165.75	$165.70
Purchase #6	$98.72	10.253%	$108.8418	$108.84	$108.85	$108.80
Purchase #7	$148.60	5.251%	$156.403	$156.40	$156.40	$156.40
7 purchase totals =	$739.21		$801.4246	$801.42	$801.45	$801.40