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	$38.63	6.682%	$41.2113	$41.21	$41.20	$41.20
Purchase #2	$151.80	13.831%	$172.7955	$172.80	$172.80	$172.80
Purchase #3	$240.52	6.285%	$255.6367	$255.64	$255.65	$255.60
Purchase #4	$167.92	13.356%	$190.3474	$190.35	$190.35	$190.30
Purchase #5	$18.34	5.370%	$19.3249	$19.32	$19.30	$19.30
Purchase #6	$137.41	13.677%	$156.2036	$156.20	$156.20	$156.20
Purchase #7	$238.83	11.738%	$266.8639	$266.86	$266.85	$266.90
7 purchase totals =	$993.45		$1,102.3833	$1,102.38	$1,102.35	$1,102.30