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	$102.57	8.352%	$111.1366	$111.14	$111.15	$111.10
Purchase #2	$54.57	6.815%	$58.2889	$58.29	$58.30	$58.30
Purchase #3	$197.31	4.645%	$206.475	$206.48	$206.50	$206.50
Purchase #4	$18.55	9.510%	$20.3141	$20.31	$20.30	$20.30
Purchase #5	$41.57	13.657%	$47.2472	$47.25	$47.25	$47.20
Purchase #6	$18.46	4.570%	$19.3036	$19.30	$19.30	$19.30
Purchase #7	$38.73	12.346%	$43.5116	$43.51	$43.50	$43.50
7 purchase totals =	$471.76		$506.2770	$506.28	$506.30	$506.20