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	$140.75	13.386%	$159.5908	$159.59	$159.60	$159.60
Purchase #2	$71.53	7.324%	$76.7689	$76.77	$76.75	$76.80
Purchase #3	$118.60	13.548%	$134.6679	$134.67	$134.65	$134.70
Purchase #4	$82.32	8.112%	$88.9978	$89.00	$89.00	$89.00
Purchase #5	$103.28	8.180%	$111.7283	$111.73	$111.75	$111.70
Purchase #6	$64.74	8.493%	$70.2384	$70.24	$70.25	$70.20
Purchase #7	$167.92	12.418%	$188.7723	$188.77	$188.75	$188.80
7 purchase totals =	$749.14		$830.7644	$830.77	$830.75	$830.80