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	$165.92	12.267%	$186.2734	$186.27	$186.25	$186.30
Purchase #2	$121.78	7.164%	$130.5043	$130.50	$130.50	$130.50
Purchase #3	$224.63	10.466%	$248.1398	$248.14	$248.15	$248.10
Purchase #4	$141.83	9.644%	$155.5081	$155.51	$155.50	$155.50
Purchase #5	$25.45	4.487%	$26.5919	$26.59	$26.60	$26.60
Purchase #6	$81.64	11.168%	$90.7576	$90.76	$90.75	$90.80
Purchase #7	$6.76	7.851%	$7.2907	$7.29	$7.30	$7.30
7 purchase totals =	$768.01		$845.0658	$845.06	$845.05	$845.10