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	$104.68	12.247%	$117.5002	$117.50	$117.50	$117.50
Purchase #2	$138.89	5.156%	$146.0512	$146.05	$146.05	$146.10
Purchase #3	$213.80	5.314%	$225.1613	$225.16	$225.15	$225.20
Purchase #4	$99.73	10.699%	$110.4001	$110.40	$110.40	$110.40
Purchase #5	$98.90	12.750%	$111.5098	$111.51	$111.50	$111.50
Purchase #6	$152.74	11.458%	$170.2409	$170.24	$170.25	$170.20
Purchase #7	$81.68	10.502%	$90.258	$90.26	$90.25	$90.30
7 purchase totals =	$890.42		$971.1215	$971.12	$971.10	$971.20