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	$50.43	4.688%	$52.7942	$52.79	$52.80	$52.80
Purchase #2	$51.81	11.732%	$57.8883	$57.89	$57.90	$57.90
Purchase #3	$172.92	10.386%	$190.8795	$190.88	$190.90	$190.90
Purchase #4	$171.88	11.489%	$191.6273	$191.63	$191.65	$191.60
Purchase #5	$63.58	5.406%	$67.0171	$67.02	$67.00	$67.00
Purchase #6	$98.45	13.318%	$111.5616	$111.56	$111.55	$111.60
Purchase #7	$218.29	13.626%	$248.0342	$248.03	$248.05	$248.00
7 purchase totals =	$827.36		$919.8022	$919.80	$919.85	$919.80