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	$124.27	13.590%	$141.1583	$141.16	$141.15	$141.20
Purchase #2	$233.59	12.781%	$263.4451	$263.45	$263.45	$263.40
Purchase #3	$70.52	10.707%	$78.0706	$78.07	$78.05	$78.10
Purchase #4	$59.30	9.868%	$65.1517	$65.15	$65.15	$65.20
Purchase #5	$219.38	9.191%	$239.5432	$239.54	$239.55	$239.50
Purchase #6	$207.45	6.452%	$220.8347	$220.83	$220.85	$220.80
Purchase #7	$11.87	4.590%	$12.4148	$12.41	$12.40	$12.40
7 purchase totals =	$926.38		$1,020.6184	$1,020.61	$1,020.60	$1,020.60