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	$147.90	12.496%	$166.3816	$166.38	$166.40	$166.40
Purchase #2	$99.80	5.516%	$105.305	$105.31	$105.30	$105.30
Purchase #3	$36.92	5.748%	$39.0422	$39.04	$39.05	$39.00
Purchase #4	$81.54	13.102%	$92.2234	$92.22	$92.20	$92.20
Purchase #5	$103.51	13.866%	$117.8627	$117.86	$117.85	$117.90
Purchase #6	$247.75	8.315%	$268.3504	$268.35	$268.35	$268.40
Purchase #7	$59.46	10.219%	$65.5362	$65.54	$65.55	$65.50
7 purchase totals =	$776.88		$854.7015	$854.70	$854.70	$854.70