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	$64.28	4.387%	$67.1	$67.10	$67.10	$67.10
Purchase #2	$88.57	12.638%	$99.7635	$99.76	$99.75	$99.80
Purchase #3	$96.39	9.377%	$105.4285	$105.43	$105.45	$105.40
Purchase #4	$204.77	11.152%	$227.606	$227.61	$227.60	$227.60
Purchase #5	$82.80	10.780%	$91.7258	$91.73	$91.75	$91.70
Purchase #6	$103.73	4.394%	$108.2879	$108.29	$108.30	$108.30
Purchase #7	$24.93	7.413%	$26.7781	$26.78	$26.80	$26.80
7 purchase totals =	$665.47		$726.6898	$726.70	$726.75	$726.70