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	$9.84	4.796%	$10.3119	$10.31	$10.30	$10.30
Purchase #2	$109.41	6.750%	$116.7952	$116.80	$116.80	$116.80
Purchase #3	$59.74	4.458%	$62.4032	$62.40	$62.40	$62.40
Purchase #4	$9.98	8.565%	$10.8348	$10.83	$10.85	$10.80
Purchase #5	$215.28	12.113%	$241.3569	$241.36	$241.35	$241.40
Purchase #6	$133.46	12.434%	$150.0544	$150.05	$150.05	$150.10
Purchase #7	$79.92	11.721%	$89.2874	$89.29	$89.30	$89.30
7 purchase totals =	$617.63		$681.0438	$681.04	$681.05	$681.10