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	$223.74	10.227%	$246.6219	$246.62	$246.60	$246.60
Purchase #2	$151.93	10.778%	$168.305	$168.31	$168.30	$168.30
Purchase #3	$247.47	11.493%	$275.9117	$275.91	$275.90	$275.90
Purchase #4	$29.79	10.106%	$32.8006	$32.80	$32.80	$32.80
Purchase #5	$132.54	3.686%	$137.4254	$137.43	$137.45	$137.40
Purchase #6	$29.84	3.533%	$30.8942	$30.89	$30.90	$30.90
Purchase #7	$201.50	11.130%	$223.927	$223.93	$223.95	$223.90
7 purchase totals =	$1,016.81		$1,115.8858	$1,115.89	$1,115.90	$1,115.80