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	$96.59	4.340%	$100.782	$100.78	$100.80	$100.80
Purchase #2	$237.54	13.348%	$269.2468	$269.25	$269.25	$269.20
Purchase #3	$122.47	13.834%	$139.4125	$139.41	$139.40	$139.40
Purchase #4	$49.89	11.111%	$55.4333	$55.43	$55.45	$55.40
Purchase #5	$244.59	9.235%	$267.1779	$267.18	$267.20	$267.20
Purchase #6	$205.92	11.347%	$229.2857	$229.29	$229.30	$229.30
Purchase #7	$7.59	3.174%	$7.8309	$7.83	$7.85	$7.80
7 purchase totals =	$964.59		$1,069.1691	$1,069.17	$1,069.25	$1,069.10