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	$83.58	13.171%	$94.5883	$94.59	$94.60	$94.60
Purchase #2	$9.51	5.829%	$10.0643	$10.06	$10.05	$10.10
Purchase #3	$21.74	4.267%	$22.6676	$22.67	$22.65	$22.70
Purchase #4	$225.30	5.340%	$237.331	$237.33	$237.35	$237.30
Purchase #5	$103.57	7.740%	$111.5863	$111.59	$111.60	$111.60
Purchase #6	$103.72	4.858%	$108.7587	$108.76	$108.75	$108.80
Purchase #7	$78.99	7.826%	$85.1718	$85.17	$85.15	$85.20
7 purchase totals =	$626.41		$670.1680	$670.17	$670.15	$670.30