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	$67.58	5.629%	$71.3841	$71.38	$71.40	$71.40
Purchase #2	$47.63	10.355%	$52.5621	$52.56	$52.55	$52.60
Purchase #3	$143.42	9.854%	$157.5526	$157.55	$157.55	$157.60
Purchase #4	$114.39	8.232%	$123.8066	$123.81	$123.80	$123.80
Purchase #5	$78.60	4.154%	$81.865	$81.87	$81.85	$81.90
Purchase #6	$74.82	10.189%	$82.4434	$82.44	$82.45	$82.40
Purchase #7	$67.76	11.502%	$75.5538	$75.55	$75.55	$75.60
7 purchase totals =	$594.20		$645.1676	$645.16	$645.15	$645.30