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	$89.26	12.833%	$100.7147	$100.71	$100.70	$100.70
Purchase #2	$211.95	10.447%	$234.0924	$234.09	$234.10	$234.10
Purchase #3	$213.43	13.551%	$242.3519	$242.35	$242.35	$242.40
Purchase #4	$37.53	4.858%	$39.3532	$39.35	$39.35	$39.40
Purchase #5	$11.47	13.855%	$13.0592	$13.06	$13.05	$13.10
Purchase #6	$104.56	4.536%	$109.3028	$109.30	$109.30	$109.30
Purchase #7	$52.92	3.464%	$54.7531	$54.75	$54.75	$54.80
7 purchase totals =	$721.12		$793.6273	$793.61	$793.60	$793.80