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	$38.83	6.559%	$41.3769	$41.38	$41.40	$41.40
Purchase #2	$158.51	10.813%	$175.6497	$175.65	$175.65	$175.60
Purchase #3	$92.34	5.650%	$97.5572	$97.56	$97.55	$97.60
Purchase #4	$204.49	11.398%	$227.7978	$227.80	$227.80	$227.80
Purchase #5	$60.71	7.846%	$65.4733	$65.47	$65.45	$65.50
Purchase #6	$225.86	12.120%	$253.2342	$253.23	$253.25	$253.20
Purchase #7	$128.67	9.658%	$141.0969	$141.10	$141.10	$141.10
7 purchase totals =	$909.41		$1,002.1860	$1,002.19	$1,002.20	$1,002.20