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	$228.46	13.298%	$258.8406	$258.84	$258.85	$258.80
Purchase #2	$10.70	11.214%	$11.8999	$11.90	$11.90	$11.90
Purchase #3	$101.44	11.330%	$112.9332	$112.93	$112.95	$112.90
Purchase #4	$97.25	13.396%	$110.2776	$110.28	$110.30	$110.30
Purchase #5	$120.29	6.140%	$127.6758	$127.68	$127.70	$127.70
Purchase #6	$129.48	7.773%	$139.5445	$139.54	$139.55	$139.50
Purchase #7	$88.29	12.165%	$99.0305	$99.03	$99.05	$99.00
7 purchase totals =	$775.91		$860.2021	$860.20	$860.30	$860.10