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	$49.58	10.128%	$54.6015	$54.60	$54.60	$54.60
Purchase #2	$151.36	7.564%	$162.8089	$162.81	$162.80	$162.80
Purchase #3	$15.82	12.618%	$17.8162	$17.82	$17.80	$17.80
Purchase #4	$79.56	11.106%	$88.3959	$88.40	$88.40	$88.40
Purchase #5	$11.81	6.388%	$12.5644	$12.56	$12.55	$12.60
Purchase #6	$78.63	4.540%	$82.1998	$82.20	$82.20	$82.20
Purchase #7	$218.86	11.221%	$243.4183	$243.42	$243.40	$243.40
7 purchase totals =	$605.62		$661.8050	$661.81	$661.75	$661.80