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	$135.84	7.814%	$146.4545	$146.45	$146.45	$146.50
Purchase #2	$176.86	5.154%	$185.9754	$185.98	$186.00	$186.00
Purchase #3	$90.42	10.411%	$99.8336	$99.83	$99.85	$99.80
Purchase #4	$205.67	6.543%	$219.127	$219.13	$219.15	$219.10
Purchase #5	$130.37	3.252%	$134.6096	$134.61	$134.60	$134.60
Purchase #6	$17.40	9.726%	$19.0923	$19.09	$19.10	$19.10
Purchase #7	$56.76	4.253%	$59.174	$59.17	$59.15	$59.20
7 purchase totals =	$813.32		$864.2664	$864.26	$864.30	$864.30