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	$38.37	5.638%	$40.5333	$40.53	$40.55	$40.50
Purchase #2	$101.59	6.453%	$108.1456	$108.15	$108.15	$108.10
Purchase #3	$142.28	4.594%	$148.8163	$148.82	$148.80	$148.80
Purchase #4	$150.71	4.675%	$157.7557	$157.76	$157.75	$157.80
Purchase #5	$74.34	10.745%	$82.3278	$82.33	$82.35	$82.30
Purchase #6	$99.59	6.272%	$105.8363	$105.84	$105.85	$105.80
Purchase #7	$73.98	12.374%	$83.1343	$83.13	$83.15	$83.10
7 purchase totals =	$680.86		$726.5493	$726.56	$726.60	$726.40