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	$9.66	7.854%	$10.4187	$10.42	$10.40	$10.40
Purchase #2	$232.86	9.468%	$254.9072	$254.91	$254.90	$254.90
Purchase #3	$40.38	11.106%	$44.8646	$44.86	$44.85	$44.90
Purchase #4	$158.52	8.277%	$171.6407	$171.64	$171.65	$171.60
Purchase #5	$89.65	12.708%	$101.0427	$101.04	$101.05	$101.00
Purchase #6	$92.73	13.470%	$105.2207	$105.22	$105.20	$105.20
Purchase #7	$150.61	5.154%	$158.3724	$158.37	$158.35	$158.40
7 purchase totals =	$774.41		$846.4670	$846.46	$846.40	$846.40