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	$49.33	9.692%	$54.1111	$54.11	$54.10	$54.10
Purchase #2	$133.85	9.407%	$146.4413	$146.44	$146.45	$146.40
Purchase #3	$19.38	10.690%	$21.4517	$21.45	$21.45	$21.50
Purchase #4	$36.79	9.393%	$40.2457	$40.25	$40.25	$40.20
Purchase #5	$53.89	4.162%	$56.1329	$56.13	$56.15	$56.10
Purchase #6	$51.83	10.750%	$57.4017	$57.40	$57.40	$57.40
Purchase #7	$74.68	7.279%	$80.116	$80.12	$80.10	$80.10
7 purchase totals =	$419.75		$455.9004	$455.90	$455.90	$455.80