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	$150.86	4.258%	$157.2836	$157.28	$157.30	$157.30
Purchase #2	$100.78	6.711%	$107.5433	$107.54	$107.55	$107.50
Purchase #3	$202.35	4.268%	$210.9863	$210.99	$211.00	$211.00
Purchase #4	$165.83	10.285%	$182.8856	$182.89	$182.90	$182.90
Purchase #5	$11.41	12.749%	$12.8647	$12.86	$12.85	$12.90
Purchase #6	$153.59	12.588%	$172.9239	$172.92	$172.90	$172.90
Purchase #7	$101.63	10.301%	$112.0989	$112.10	$112.10	$112.10
7 purchase totals =	$886.45		$956.5863	$956.58	$956.60	$956.60