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	$66.89	6.397%	$71.169	$71.17	$71.15	$71.20
Purchase #2	$246.78	3.381%	$255.1236	$255.12	$255.10	$255.10
Purchase #3	$31.42	11.215%	$34.9438	$34.94	$34.95	$34.90
Purchase #4	$66.90	11.843%	$74.823	$74.82	$74.80	$74.80
Purchase #5	$248.48	8.387%	$269.32	$269.32	$269.30	$269.30
Purchase #6	$85.29	5.336%	$89.8411	$89.84	$89.85	$89.80
Purchase #7	$12.28	12.603%	$13.8276	$13.83	$13.85	$13.80
7 purchase totals =	$758.04		$809.0481	$809.04	$809.00	$808.90