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	$36.91	13.771%	$41.9929	$41.99	$42.00	$42.00
Purchase #2	$157.78	13.295%	$178.7569	$178.76	$178.75	$178.80
Purchase #3	$54.64	13.229%	$61.8683	$61.87	$61.85	$61.90
Purchase #4	$166.79	11.370%	$185.754	$185.75	$185.75	$185.80
Purchase #5	$52.44	4.774%	$54.9435	$54.94	$54.95	$54.90
Purchase #6	$99.50	5.320%	$104.7934	$104.79	$104.80	$104.80
Purchase #7	$63.48	10.810%	$70.3422	$70.34	$70.35	$70.30
7 purchase totals =	$631.54		$698.4512	$698.44	$698.45	$698.50