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	$93.42	8.275%	$101.1505	$101.15	$101.15	$101.20
Purchase #2	$145.55	5.741%	$153.906	$153.91	$153.90	$153.90
Purchase #3	$19.71	11.573%	$21.991	$21.99	$22.00	$22.00
Purchase #4	$156.67	10.406%	$172.9731	$172.97	$172.95	$173.00
Purchase #5	$78.61	6.494%	$83.7149	$83.71	$83.70	$83.70
Purchase #6	$42.65	5.730%	$45.0938	$45.09	$45.10	$45.10
Purchase #7	$76.54	7.192%	$82.0448	$82.04	$82.05	$82.00
7 purchase totals =	$613.15		$660.8741	$660.86	$660.85	$660.90