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	$17.25	10.131%	$18.9976	$19.00	$19.00	$19.00
Purchase #2	$38.47	11.513%	$42.8991	$42.90	$42.90	$42.90
Purchase #3	$164.84	10.325%	$181.8597	$181.86	$181.85	$181.90
Purchase #4	$188.97	8.556%	$205.1383	$205.14	$205.15	$205.10
Purchase #5	$33.41	5.294%	$35.1787	$35.18	$35.20	$35.20
Purchase #6	$51.36	9.643%	$56.3126	$56.31	$56.30	$56.30
Purchase #7	$100.28	9.614%	$109.9209	$109.92	$109.90	$109.90
7 purchase totals =	$594.58		$650.3069	$650.31	$650.30	$650.30