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	$107.33	4.832%	$112.5162	$112.52	$112.50	$112.50
Purchase #2	$158.34	9.377%	$173.1875	$173.19	$173.20	$173.20
Purchase #3	$133.31	8.732%	$144.9506	$144.95	$144.95	$145.00
Purchase #4	$40.33	13.160%	$45.6374	$45.64	$45.65	$45.60
Purchase #5	$53.45	11.264%	$59.4706	$59.47	$59.45	$59.50
Purchase #6	$121.74	10.816%	$134.9074	$134.91	$134.90	$134.90
Purchase #7	$219.92	12.864%	$248.2105	$248.21	$248.20	$248.20
7 purchase totals =	$834.42		$918.8802	$918.89	$918.85	$918.90