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	$103.55	12.782%	$116.7858	$116.79	$116.80	$116.80
Purchase #2	$87.51	3.329%	$90.4232	$90.42	$90.40	$90.40
Purchase #3	$188.37	11.870%	$210.7295	$210.73	$210.75	$210.70
Purchase #4	$105.82	7.487%	$113.7427	$113.74	$113.75	$113.70
Purchase #5	$58.56	12.395%	$65.8185	$65.82	$65.80	$65.80
Purchase #6	$115.48	4.598%	$120.7898	$120.79	$120.80	$120.80
Purchase #7	$184.75	13.654%	$209.9758	$209.98	$210.00	$210.00
7 purchase totals =	$844.04		$928.2653	$928.27	$928.30	$928.20