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	$10.28	11.143%	$11.4255	$11.43	$11.45	$11.40
Purchase #2	$197.60	9.166%	$215.712	$215.71	$215.70	$215.70
Purchase #3	$176.68	3.646%	$183.1218	$183.12	$183.10	$183.10
Purchase #4	$38.47	13.176%	$43.5388	$43.54	$43.55	$43.50
Purchase #5	$105.51	5.513%	$111.3268	$111.33	$111.35	$111.30
Purchase #6	$35.47	10.617%	$39.2358	$39.24	$39.25	$39.20
Purchase #7	$107.55	12.400%	$120.8862	$120.89	$120.90	$120.90
7 purchase totals =	$671.56		$725.2469	$725.26	$725.30	$725.10