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	$38.76	5.578%	$40.922	$40.92	$40.90	$40.90
Purchase #2	$60.31	8.305%	$65.3187	$65.32	$65.30	$65.30
Purchase #3	$155.44	6.250%	$165.155	$165.16	$165.15	$165.20
Purchase #4	$74.86	3.853%	$77.7444	$77.74	$77.75	$77.70
Purchase #5	$46.91	5.691%	$49.5796	$49.58	$49.60	$49.60
Purchase #6	$95.73	3.792%	$99.3601	$99.36	$99.35	$99.40
Purchase #7	$18.49	9.241%	$20.1987	$20.20	$20.20	$20.20
7 purchase totals =	$490.50		$518.2785	$518.28	$518.25	$518.30