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	$190.74	9.271%	$208.4235	$208.42	$208.40	$208.40
Purchase #2	$240.94	3.112%	$248.4381	$248.44	$248.45	$248.40
Purchase #3	$15.85	13.389%	$17.9722	$17.97	$17.95	$18.00
Purchase #4	$80.57	11.201%	$89.5946	$89.59	$89.60	$89.60
Purchase #5	$59.49	10.288%	$65.6103	$65.61	$65.60	$65.60
Purchase #6	$153.59	8.245%	$166.2535	$166.25	$166.25	$166.30
Purchase #7	$170.91	7.836%	$184.3025	$184.30	$184.30	$184.30
7 purchase totals =	$912.09		$980.5947	$980.58	$980.55	$980.60