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	$39.64	9.308%	$43.3297	$43.33	$43.35	$43.30
Purchase #2	$99.80	3.216%	$103.0096	$103.01	$103.00	$103.00
Purchase #3	$41.39	9.480%	$45.3138	$45.31	$45.30	$45.30
Purchase #4	$138.52	5.380%	$145.9724	$145.97	$145.95	$146.00
Purchase #5	$116.90	12.722%	$131.772	$131.77	$131.75	$131.80
Purchase #6	$132.97	13.369%	$150.7468	$150.75	$150.75	$150.70
Purchase #7	$154.80	10.300%	$170.7444	$170.74	$170.75	$170.70
7 purchase totals =	$724.02		$790.8887	$790.88	$790.85	$790.80