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	$222.32	3.363%	$229.7966	$229.80	$229.80	$229.80
Purchase #2	$238.72	7.152%	$255.7933	$255.79	$255.80	$255.80
Purchase #3	$6.67	11.153%	$7.4139	$7.41	$7.40	$7.40
Purchase #4	$219.42	10.438%	$242.3231	$242.32	$242.30	$242.30
Purchase #5	$112.52	5.478%	$118.6838	$118.68	$118.70	$118.70
Purchase #6	$37.55	12.863%	$42.3801	$42.38	$42.40	$42.40
Purchase #7	$37.94	11.698%	$42.3782	$42.38	$42.40	$42.40
7 purchase totals =	$875.14		$938.7690	$938.76	$938.80	$938.80