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	$50.37	7.381%	$54.0878	$54.09	$54.10	$54.10
Purchase #2	$234.69	8.501%	$254.641	$254.64	$254.65	$254.60
Purchase #3	$112.90	5.265%	$118.8442	$118.84	$118.85	$118.80
Purchase #4	$125.74	7.130%	$134.7053	$134.71	$134.70	$134.70
Purchase #5	$37.77	13.465%	$42.8557	$42.86	$42.85	$42.90
Purchase #6	$10.41	3.805%	$10.8061	$10.81	$10.80	$10.80
Purchase #7	$113.77	8.126%	$123.015	$123.02	$123.00	$123.00
7 purchase totals =	$685.65		$738.9551	$738.97	$738.95	$738.90