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	$20.39	9.312%	$22.2887	$22.29	$22.30	$22.30
Purchase #2	$220.35	10.202%	$242.8301	$242.83	$242.85	$242.80
Purchase #3	$192.80	13.770%	$219.3486	$219.35	$219.35	$219.30
Purchase #4	$64.38	4.784%	$67.4599	$67.46	$67.45	$67.50
Purchase #5	$84.57	13.667%	$96.1282	$96.13	$96.15	$96.10
Purchase #6	$67.78	7.605%	$72.9347	$72.93	$72.95	$72.90
Purchase #7	$132.76	11.280%	$147.7353	$147.74	$147.75	$147.70
7 purchase totals =	$783.03		$868.7255	$868.73	$868.80	$868.60