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	$108.85	4.448%	$113.6916	$113.69	$113.70	$113.70
Purchase #2	$97.79	13.776%	$111.2616	$111.26	$111.25	$111.30
Purchase #3	$163.74	12.294%	$183.8702	$183.87	$183.85	$183.90
Purchase #4	$89.76	10.633%	$99.3042	$99.30	$99.30	$99.30
Purchase #5	$130.47	12.159%	$146.3338	$146.33	$146.35	$146.30
Purchase #6	$230.66	11.420%	$257.0014	$257.00	$257.00	$257.00
Purchase #7	$53.78	10.473%	$59.4124	$59.41	$59.40	$59.40
7 purchase totals =	$875.05		$970.8752	$970.86	$970.85	$970.90