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	$152.69	12.761%	$172.1748	$172.17	$172.15	$172.20
Purchase #2	$205.99	8.102%	$222.6793	$222.68	$222.70	$222.70
Purchase #3	$89.75	7.136%	$96.1546	$96.15	$96.15	$96.20
Purchase #4	$161.83	4.771%	$169.5509	$169.55	$169.55	$169.60
Purchase #5	$80.26	11.309%	$89.3366	$89.34	$89.35	$89.30
Purchase #6	$62.61	13.153%	$70.8451	$70.85	$70.85	$70.80
Purchase #7	$27.35	8.162%	$29.5823	$29.58	$29.60	$29.60
7 purchase totals =	$780.48		$850.3236	$850.32	$850.35	$850.40