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	$18.66	6.664%	$19.9035	$19.90	$19.90	$19.90
Purchase #2	$90.55	9.713%	$99.3451	$99.35	$99.35	$99.30
Purchase #3	$217.67	8.845%	$236.9229	$236.92	$236.90	$236.90
Purchase #4	$233.94	4.364%	$244.1491	$244.15	$244.15	$244.10
Purchase #5	$96.77	4.297%	$100.9282	$100.93	$100.95	$100.90
Purchase #6	$83.28	7.196%	$89.2728	$89.27	$89.25	$89.30
Purchase #7	$34.38	10.648%	$38.0408	$38.04	$38.05	$38.00
7 purchase totals =	$775.25		$828.5624	$828.56	$828.55	$828.40