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	$235.90	13.776%	$268.3976	$268.40	$268.40	$268.40
Purchase #2	$19.64	6.301%	$20.8775	$20.88	$20.90	$20.90
Purchase #3	$188.53	5.706%	$199.2875	$199.29	$199.30	$199.30
Purchase #4	$72.59	6.236%	$77.1167	$77.12	$77.10	$77.10
Purchase #5	$42.37	8.241%	$45.8617	$45.86	$45.85	$45.90
Purchase #6	$179.62	5.173%	$188.9117	$188.91	$188.90	$188.90
Purchase #7	$25.71	12.868%	$29.0184	$29.02	$29.00	$29.00
7 purchase totals =	$764.36		$829.4711	$829.48	$829.45	$829.50