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	$211.60	13.558%	$240.2887	$240.29	$240.30	$240.30
Purchase #2	$134.63	6.593%	$143.5062	$143.51	$143.50	$143.50
Purchase #3	$140.72	10.372%	$155.3155	$155.32	$155.30	$155.30
Purchase #4	$13.30	7.412%	$14.2858	$14.29	$14.30	$14.30
Purchase #5	$181.99	12.301%	$204.3766	$204.38	$204.40	$204.40
Purchase #6	$37.49	13.336%	$42.4897	$42.49	$42.50	$42.50
Purchase #7	$13.83	10.502%	$15.2824	$15.28	$15.30	$15.30
7 purchase totals =	$733.56		$815.5449	$815.56	$815.60	$815.60