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	$81.74	10.260%	$90.1265	$90.13	$90.15	$90.10
Purchase #2	$114.68	6.222%	$121.8154	$121.82	$121.80	$121.80
Purchase #3	$137.93	3.771%	$143.1313	$143.13	$143.15	$143.10
Purchase #4	$60.43	8.547%	$65.595	$65.60	$65.60	$65.60
Purchase #5	$30.31	11.675%	$33.8487	$33.85	$33.85	$33.80
Purchase #6	$107.30	4.521%	$112.151	$112.15	$112.15	$112.20
Purchase #7	$235.93	7.834%	$254.4128	$254.41	$254.40	$254.40
7 purchase totals =	$768.32		$821.0807	$821.09	$821.10	$821.00