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	$150.86	5.112%	$158.572	$158.57	$158.55	$158.60
Purchase #2	$190.80	9.442%	$208.8153	$208.82	$208.80	$208.80
Purchase #3	$102.79	8.459%	$111.485	$111.49	$111.50	$111.50
Purchase #4	$247.25	12.559%	$278.3021	$278.30	$278.30	$278.30
Purchase #5	$71.78	9.815%	$78.8252	$78.83	$78.85	$78.80
Purchase #6	$173.76	10.280%	$191.6225	$191.62	$191.60	$191.60
Purchase #7	$123.80	3.537%	$128.1788	$128.18	$128.20	$128.20
7 purchase totals =	$1,061.04		$1,155.8009	$1,155.81	$1,155.80	$1,155.80