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	$27.81	6.379%	$29.584	$29.58	$29.60	$29.60
Purchase #2	$205.82	8.640%	$223.6028	$223.60	$223.60	$223.60
Purchase #3	$13.76	13.500%	$15.6176	$15.62	$15.60	$15.60
Purchase #4	$86.57	3.376%	$89.4926	$89.49	$89.50	$89.50
Purchase #5	$35.90	7.409%	$38.5598	$38.56	$38.55	$38.60
Purchase #6	$22.91	9.184%	$25.0141	$25.01	$25.00	$25.00
Purchase #7	$171.28	10.151%	$188.6666	$188.67	$188.65	$188.70
7 purchase totals =	$564.05		$610.5375	$610.53	$610.50	$610.60