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	$205.51	3.325%	$212.3432	$212.34	$212.35	$212.30
Purchase #2	$180.70	5.316%	$190.306	$190.31	$190.30	$190.30
Purchase #3	$94.91	6.211%	$100.8049	$100.80	$100.80	$100.80
Purchase #4	$32.31	7.809%	$34.8331	$34.83	$34.85	$34.80
Purchase #5	$20.41	9.700%	$22.3898	$22.39	$22.40	$22.40
Purchase #6	$226.74	13.162%	$256.5835	$256.58	$256.60	$256.60
Purchase #7	$58.59	7.168%	$62.7897	$62.79	$62.80	$62.80
7 purchase totals =	$819.17		$880.0502	$880.04	$880.10	$880.00