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	$19.65	5.179%	$20.6677	$20.67	$20.65	$20.70
Purchase #2	$212.74	13.297%	$241.028	$241.03	$241.05	$241.00
Purchase #3	$154.76	12.111%	$173.503	$173.50	$173.50	$173.50
Purchase #4	$72.79	8.275%	$78.8134	$78.81	$78.80	$78.80
Purchase #5	$28.60	3.281%	$29.5384	$29.54	$29.55	$29.50
Purchase #6	$55.70	10.523%	$61.5613	$61.56	$61.55	$61.60
Purchase #7	$93.95	6.457%	$100.0164	$100.02	$100.00	$100.00
7 purchase totals =	$638.19		$705.1282	$705.13	$705.10	$705.10