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	$172.36	8.489%	$186.9916	$186.99	$187.00	$187.00
Purchase #2	$137.52	10.188%	$151.5305	$151.53	$151.55	$151.50
Purchase #3	$233.25	10.722%	$258.2591	$258.26	$258.25	$258.30
Purchase #4	$70.61	8.431%	$76.5631	$76.56	$76.55	$76.60
Purchase #5	$78.85	13.696%	$89.6493	$89.65	$89.65	$89.60
Purchase #6	$8.44	6.159%	$8.9598	$8.96	$8.95	$9.00
Purchase #7	$188.89	9.309%	$206.4738	$206.47	$206.45	$206.50
7 purchase totals =	$889.92		$978.4272	$978.42	$978.40	$978.50