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	$103.37	5.736%	$109.2993	$109.30	$109.30	$109.30
Purchase #2	$177.91	10.333%	$196.2934	$196.29	$196.30	$196.30
Purchase #3	$29.35	8.570%	$31.8653	$31.87	$31.85	$31.90
Purchase #4	$212.54	6.116%	$225.5389	$225.54	$225.55	$225.50
Purchase #5	$231.64	12.286%	$260.0993	$260.10	$260.10	$260.10
Purchase #6	$103.38	7.640%	$111.2782	$111.28	$111.30	$111.30
Purchase #7	$204.51	10.738%	$226.4703	$226.47	$226.45	$226.50
7 purchase totals =	$1,062.70		$1,160.8447	$1,160.85	$1,160.85	$1,160.90