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	$95.35	5.732%	$100.8155	$100.82	$100.80	$100.80
Purchase #2	$239.48	13.719%	$272.3343	$272.33	$272.35	$272.30
Purchase #3	$231.72	11.682%	$258.7895	$258.79	$258.80	$258.80
Purchase #4	$6.50	10.568%	$7.1869	$7.19	$7.20	$7.20
Purchase #5	$72.47	9.808%	$79.5779	$79.58	$79.60	$79.60
Purchase #6	$116.86	11.739%	$130.5782	$130.58	$130.60	$130.60
Purchase #7	$240.92	8.137%	$260.5237	$260.52	$260.50	$260.50
7 purchase totals =	$1,003.30		$1,109.8060	$1,109.81	$1,109.85	$1,109.80