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	$170.96	4.200%	$178.1403	$178.14	$178.15	$178.10
Purchase #2	$45.96	7.239%	$49.287	$49.29	$49.30	$49.30
Purchase #3	$45.95	8.186%	$49.7115	$49.71	$49.70	$49.70
Purchase #4	$174.74	7.290%	$187.4785	$187.48	$187.50	$187.50
Purchase #5	$62.98	13.219%	$71.3053	$71.31	$71.30	$71.30
Purchase #6	$242.29	5.565%	$255.7734	$255.77	$255.75	$255.80
Purchase #7	$88.90	12.227%	$99.7698	$99.77	$99.75	$99.80
7 purchase totals =	$831.78		$891.4658	$891.47	$891.45	$891.50