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	$89.72	10.714%	$99.3326	$99.33	$99.35	$99.30
Purchase #2	$218.36	4.595%	$228.3936	$228.39	$228.40	$228.40
Purchase #3	$216.36	11.602%	$241.4621	$241.46	$241.45	$241.50
Purchase #4	$48.98	10.765%	$54.2527	$54.25	$54.25	$54.30
Purchase #5	$47.77	3.188%	$49.2929	$49.29	$49.30	$49.30
Purchase #6	$183.27	6.565%	$195.3017	$195.30	$195.30	$195.30
Purchase #7	$239.50	13.725%	$272.3714	$272.37	$272.35	$272.40
7 purchase totals =	$1,043.96		$1,140.4070	$1,140.39	$1,140.40	$1,140.50