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	$190.28	13.140%	$215.2828	$215.28	$215.30	$215.30
Purchase #2	$145.61	13.258%	$164.915	$164.92	$164.90	$164.90
Purchase #3	$240.54	6.531%	$256.2497	$256.25	$256.25	$256.20
Purchase #4	$123.90	5.318%	$130.489	$130.49	$130.50	$130.50
Purchase #5	$240.94	10.228%	$265.5833	$265.58	$265.60	$265.60
Purchase #6	$232.79	10.280%	$256.7208	$256.72	$256.70	$256.70
Purchase #7	$133.46	12.466%	$150.0971	$150.10	$150.10	$150.10
7 purchase totals =	$1,307.52		$1,439.3377	$1,439.34	$1,439.35	$1,439.30