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	$174.57	3.856%	$181.3014	$181.30	$181.30	$181.30
Purchase #2	$55.42	6.460%	$59.0001	$59.00	$59.00	$59.00
Purchase #3	$80.84	9.569%	$88.5756	$88.58	$88.60	$88.60
Purchase #4	$32.55	9.284%	$35.5719	$35.57	$35.55	$35.60
Purchase #5	$167.68	13.225%	$189.8557	$189.86	$189.85	$189.90
Purchase #6	$205.96	5.597%	$217.4876	$217.49	$217.50	$217.50
Purchase #7	$114.85	3.155%	$118.4735	$118.47	$118.45	$118.50
7 purchase totals =	$831.87		$890.2658	$890.27	$890.25	$890.40