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	$171.81	10.857%	$190.4634	$190.46	$190.45	$190.50
Purchase #2	$76.47	8.401%	$82.8942	$82.89	$82.90	$82.90
Purchase #3	$74.30	12.824%	$83.8282	$83.83	$83.85	$83.80
Purchase #4	$70.71	9.128%	$77.1644	$77.16	$77.15	$77.20
Purchase #5	$82.56	7.450%	$88.7107	$88.71	$88.70	$88.70
Purchase #6	$163.83	10.126%	$180.4194	$180.42	$180.40	$180.40
Purchase #7	$245.51	7.235%	$263.2726	$263.27	$263.25	$263.30
7 purchase totals =	$885.19		$966.7529	$966.74	$966.70	$966.80