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	$90.75	13.786%	$103.2608	$103.26	$103.25	$103.30
Purchase #2	$157.55	9.593%	$172.6638	$172.66	$172.65	$172.70
Purchase #3	$224.29	12.321%	$251.9248	$251.92	$251.90	$251.90
Purchase #4	$161.41	6.227%	$171.461	$171.46	$171.45	$171.50
Purchase #5	$18.92	5.183%	$19.9006	$19.90	$19.90	$19.90
Purchase #6	$10.75	7.778%	$11.5861	$11.59	$11.60	$11.60
Purchase #7	$56.92	9.513%	$62.3348	$62.33	$62.35	$62.30
7 purchase totals =	$720.59		$793.1319	$793.12	$793.10	$793.20