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	$230.33	8.288%	$249.4198	$249.42	$249.40	$249.40
Purchase #2	$60.34	10.659%	$66.7716	$66.77	$66.75	$66.80
Purchase #3	$71.46	9.317%	$78.1179	$78.12	$78.10	$78.10
Purchase #4	$246.72	8.420%	$267.4938	$267.49	$267.50	$267.50
Purchase #5	$199.49	9.333%	$218.1084	$218.11	$218.10	$218.10
Purchase #6	$47.95	10.753%	$53.1061	$53.11	$53.10	$53.10
Purchase #7	$107.88	3.403%	$111.5512	$111.55	$111.55	$111.60
7 purchase totals =	$964.17		$1,044.5688	$1,044.57	$1,044.50	$1,044.60