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	$118.31	11.772%	$132.2375	$132.24	$132.25	$132.20
Purchase #2	$77.55	12.779%	$87.4601	$87.46	$87.45	$87.50
Purchase #3	$116.31	10.499%	$128.5214	$128.52	$128.50	$128.50
Purchase #4	$144.64	3.798%	$150.1334	$150.13	$150.15	$150.10
Purchase #5	$78.77	10.153%	$86.7675	$86.77	$86.75	$86.80
Purchase #6	$40.62	11.627%	$45.3429	$45.34	$45.35	$45.30
Purchase #7	$134.95	12.205%	$151.4206	$151.42	$151.40	$151.40
7 purchase totals =	$711.15		$781.8834	$781.88	$781.85	$781.80