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	$17.97	12.400%	$20.1983	$20.20	$20.20	$20.20
Purchase #2	$40.46	4.406%	$42.2427	$42.24	$42.25	$42.20
Purchase #3	$195.32	7.619%	$210.2014	$210.20	$210.20	$210.20
Purchase #4	$90.66	10.764%	$100.4186	$100.42	$100.40	$100.40
Purchase #5	$13.37	3.611%	$13.8528	$13.85	$13.85	$13.90
Purchase #6	$54.48	10.170%	$60.0206	$60.02	$60.00	$60.00
Purchase #7	$38.46	5.724%	$40.6615	$40.66	$40.65	$40.70
7 purchase totals =	$450.72		$487.5959	$487.59	$487.55	$487.60