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	$111.45	13.626%	$126.6362	$126.64	$126.65	$126.60
Purchase #2	$128.76	11.744%	$143.8816	$143.88	$143.90	$143.90
Purchase #3	$72.39	13.691%	$82.3009	$82.30	$82.30	$82.30
Purchase #4	$105.74	8.732%	$114.9732	$114.97	$114.95	$115.00
Purchase #5	$155.76	5.837%	$164.8517	$164.85	$164.85	$164.90
Purchase #6	$99.70	3.105%	$102.7957	$102.80	$102.80	$102.80
Purchase #7	$165.97	11.832%	$185.6076	$185.61	$185.60	$185.60
7 purchase totals =	$839.77		$921.0469	$921.05	$921.05	$921.10