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	$51.30	4.276%	$53.4936	$53.49	$53.50	$53.50
Purchase #2	$116.31	13.294%	$131.7723	$131.77	$131.75	$131.80
Purchase #3	$21.28	12.862%	$24.017	$24.02	$24.00	$24.00
Purchase #4	$59.69	10.490%	$65.9515	$65.95	$65.95	$66.00
Purchase #5	$79.93	12.246%	$89.7182	$89.72	$89.70	$89.70
Purchase #6	$142.62	3.855%	$148.118	$148.12	$148.10	$148.10
Purchase #7	$75.34	8.174%	$81.4983	$81.50	$81.50	$81.50
7 purchase totals =	$546.47		$594.5689	$594.57	$594.50	$594.60