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	$131.63	12.528%	$148.1206	$148.12	$148.10	$148.10
Purchase #2	$172.78	12.564%	$194.4881	$194.49	$194.50	$194.50
Purchase #3	$53.65	11.325%	$59.7259	$59.73	$59.75	$59.70
Purchase #4	$94.38	7.202%	$101.1772	$101.18	$101.20	$101.20
Purchase #5	$111.82	3.804%	$116.0736	$116.07	$116.05	$116.10
Purchase #6	$161.63	6.431%	$172.0244	$172.02	$172.00	$172.00
Purchase #7	$25.48	7.502%	$27.3915	$27.39	$27.40	$27.40
7 purchase totals =	$751.37		$819.0013	$819.00	$819.00	$819.00