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	$18.74	3.728%	$19.4386	$19.44	$19.45	$19.40
Purchase #2	$119.87	10.589%	$132.563	$132.56	$132.55	$132.60
Purchase #3	$157.61	8.446%	$170.9217	$170.92	$170.90	$170.90
Purchase #4	$36.42	12.185%	$40.8578	$40.86	$40.85	$40.90
Purchase #5	$216.37	13.223%	$244.9806	$244.98	$245.00	$245.00
Purchase #6	$99.54	12.339%	$111.8222	$111.82	$111.80	$111.80
Purchase #7	$225.72	9.491%	$247.1431	$247.14	$247.15	$247.10
7 purchase totals =	$874.27		$967.7270	$967.72	$967.70	$967.70