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	$66.91	8.234%	$72.4194	$72.42	$72.40	$72.40
Purchase #2	$58.56	4.814%	$61.3791	$61.38	$61.40	$61.40
Purchase #3	$9.33	8.409%	$10.1146	$10.11	$10.10	$10.10
Purchase #4	$108.68	13.466%	$123.3148	$123.31	$123.30	$123.30
Purchase #5	$33.45	4.618%	$34.9947	$34.99	$35.00	$35.00
Purchase #6	$144.88	9.128%	$158.1046	$158.10	$158.10	$158.10
Purchase #7	$106.35	5.639%	$112.3471	$112.35	$112.35	$112.30
7 purchase totals =	$528.16		$572.6743	$572.66	$572.65	$572.60