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	$18.34	11.423%	$20.435	$20.44	$20.45	$20.40
Purchase #2	$148.91	4.868%	$156.1589	$156.16	$156.15	$156.20
Purchase #3	$250.52	11.118%	$278.3728	$278.37	$278.35	$278.40
Purchase #4	$184.66	9.784%	$202.7271	$202.73	$202.75	$202.70
Purchase #5	$90.86	10.156%	$100.0877	$100.09	$100.10	$100.10
Purchase #6	$205.30	8.410%	$222.5657	$222.57	$222.55	$222.60
Purchase #7	$102.76	10.233%	$113.2754	$113.28	$113.30	$113.30
7 purchase totals =	$1,001.35		$1,093.6226	$1,093.64	$1,093.65	$1,093.70