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	$159.47	7.124%	$170.8306	$170.83	$170.85	$170.80
Purchase #2	$180.91	8.498%	$196.2837	$196.28	$196.30	$196.30
Purchase #3	$240.61	7.787%	$259.3463	$259.35	$259.35	$259.30
Purchase #4	$235.87	13.729%	$268.2526	$268.25	$268.25	$268.30
Purchase #5	$97.43	5.834%	$103.1141	$103.11	$103.10	$103.10
Purchase #6	$169.45	4.161%	$176.5008	$176.50	$176.50	$176.50
Purchase #7	$112.41	3.423%	$116.2578	$116.26	$116.25	$116.30
7 purchase totals =	$1,196.15		$1,290.5859	$1,290.58	$1,290.60	$1,290.60