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	$139.59	13.514%	$158.4542	$158.45	$158.45	$158.50
Purchase #2	$164.41	10.249%	$181.2604	$181.26	$181.25	$181.30
Purchase #3	$79.86	4.522%	$83.4713	$83.47	$83.45	$83.50
Purchase #4	$68.75	11.786%	$76.8529	$76.85	$76.85	$76.90
Purchase #5	$42.46	13.434%	$48.1641	$48.16	$48.15	$48.20
Purchase #6	$189.45	7.869%	$204.3578	$204.36	$204.35	$204.40
Purchase #7	$112.34	4.825%	$117.7604	$117.76	$117.75	$117.80
7 purchase totals =	$796.86		$870.3211	$870.31	$870.25	$870.60