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	$60.56	10.456%	$66.8922	$66.89	$66.90	$66.90
Purchase #2	$110.57	8.676%	$120.1631	$120.16	$120.15	$120.20
Purchase #3	$38.46	10.212%	$42.3875	$42.39	$42.40	$42.40
Purchase #4	$105.46	5.505%	$111.2656	$111.27	$111.25	$111.30
Purchase #5	$131.46	5.726%	$138.9874	$138.99	$139.00	$139.00
Purchase #6	$203.72	13.688%	$231.6052	$231.61	$231.60	$231.60
Purchase #7	$195.31	13.811%	$222.2843	$222.28	$222.30	$222.30
7 purchase totals =	$845.54		$933.5853	$933.59	$933.60	$933.70