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	$27.32	9.632%	$29.9515	$29.95	$29.95	$30.00
Purchase #2	$172.38	7.709%	$185.6688	$185.67	$185.65	$185.70
Purchase #3	$8.56	3.663%	$8.8736	$8.87	$8.85	$8.90
Purchase #4	$109.36	6.610%	$116.5887	$116.59	$116.60	$116.60
Purchase #5	$19.50	9.219%	$21.2977	$21.30	$21.30	$21.30
Purchase #6	$51.65	3.610%	$53.5146	$53.51	$53.50	$53.50
Purchase #7	$143.84	10.449%	$158.8698	$158.87	$158.85	$158.90
7 purchase totals =	$532.61		$574.7647	$574.76	$574.70	$574.90