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	$54.57	10.518%	$60.3097	$60.31	$60.30	$60.30
Purchase #2	$91.41	12.752%	$103.0666	$103.07	$103.05	$103.10
Purchase #3	$165.45	13.278%	$187.4185	$187.42	$187.40	$187.40
Purchase #4	$74.59	3.714%	$77.3603	$77.36	$77.35	$77.40
Purchase #5	$95.98	9.712%	$105.3016	$105.30	$105.30	$105.30
Purchase #6	$58.79	11.209%	$65.3798	$65.38	$65.40	$65.40
Purchase #7	$54.39	8.491%	$59.0083	$59.01	$59.00	$59.00
7 purchase totals =	$595.18		$657.8448	$657.85	$657.80	$657.90