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	$141.85	3.348%	$146.5991	$146.60	$146.60	$146.60
Purchase #2	$86.62	6.289%	$92.0675	$92.07	$92.05	$92.10
Purchase #3	$121.76	10.751%	$134.8504	$134.85	$134.85	$134.90
Purchase #4	$79.86	11.643%	$89.1581	$89.16	$89.15	$89.20
Purchase #5	$153.75	7.665%	$165.5349	$165.53	$165.55	$165.50
Purchase #6	$156.74	5.517%	$165.3873	$165.39	$165.40	$165.40
Purchase #7	$23.59	5.140%	$24.8025	$24.80	$24.80	$24.80
7 purchase totals =	$764.17		$818.3998	$818.40	$818.40	$818.50