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	$243.66	4.715%	$255.1486	$255.15	$255.15	$255.10
Purchase #2	$188.40	8.172%	$203.796	$203.80	$203.80	$203.80
Purchase #3	$161.87	13.773%	$184.1644	$184.16	$184.15	$184.20
Purchase #4	$167.49	7.343%	$179.7888	$179.79	$179.80	$179.80
Purchase #5	$138.71	12.331%	$155.8143	$155.81	$155.80	$155.80
Purchase #6	$15.69	12.465%	$17.6458	$17.65	$17.65	$17.60
Purchase #7	$78.47	13.535%	$89.0909	$89.09	$89.10	$89.10
7 purchase totals =	$994.29		$1,085.4488	$1,085.45	$1,085.45	$1,085.40