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	$34.67	3.672%	$35.9431	$35.94	$35.95	$35.90
Purchase #2	$79.83	12.712%	$89.978	$89.98	$90.00	$90.00
Purchase #3	$48.78	7.815%	$52.5922	$52.59	$52.60	$52.60
Purchase #4	$14.96	3.269%	$15.449	$15.45	$15.45	$15.40
Purchase #5	$85.43	4.329%	$89.1283	$89.13	$89.15	$89.10
Purchase #6	$77.93	12.431%	$87.6175	$87.62	$87.60	$87.60
Purchase #7	$208.61	4.355%	$217.695	$217.70	$217.70	$217.70
7 purchase totals =	$550.21		$588.4031	$588.41	$588.45	$588.30