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	$96.60	9.440%	$105.719	$105.72	$105.70	$105.70
Purchase #2	$40.56	9.651%	$44.4744	$44.47	$44.45	$44.50
Purchase #3	$73.78	9.401%	$80.7161	$80.72	$80.70	$80.70
Purchase #4	$131.67	3.520%	$136.3048	$136.30	$136.30	$136.30
Purchase #5	$153.27	4.732%	$160.5227	$160.52	$160.50	$160.50
Purchase #6	$42.54	8.471%	$46.1436	$46.14	$46.15	$46.10
Purchase #7	$10.56	3.162%	$10.8939	$10.89	$10.90	$10.90
7 purchase totals =	$548.98		$584.7745	$584.76	$584.70	$584.70