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	$165.92	10.819%	$183.8709	$183.87	$183.85	$183.90
Purchase #2	$171.37	12.694%	$193.1237	$193.12	$193.10	$193.10
Purchase #3	$99.54	6.242%	$105.7533	$105.75	$105.75	$105.80
Purchase #4	$185.52	8.660%	$201.586	$201.59	$201.60	$201.60
Purchase #5	$161.88	6.330%	$172.127	$172.13	$172.15	$172.10
Purchase #6	$51.30	3.196%	$52.9395	$52.94	$52.95	$52.90
Purchase #7	$205.49	8.231%	$222.4039	$222.40	$222.40	$222.40
7 purchase totals =	$1,041.02		$1,131.8043	$1,131.80	$1,131.80	$1,131.80