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	$133.71	12.797%	$150.8209	$150.82	$150.80	$150.80
Purchase #2	$248.86	9.300%	$272.004	$272.00	$272.00	$272.00
Purchase #3	$120.73	9.130%	$131.7526	$131.75	$131.75	$131.80
Purchase #4	$79.41	12.601%	$89.4165	$89.42	$89.40	$89.40
Purchase #5	$35.79	4.683%	$37.466	$37.47	$37.45	$37.50
Purchase #6	$164.97	11.643%	$184.1775	$184.18	$184.20	$184.20
Purchase #7	$46.28	10.420%	$51.1024	$51.10	$51.10	$51.10
7 purchase totals =	$829.75		$916.7399	$916.74	$916.70	$916.80