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	$67.86	13.302%	$76.8867	$76.89	$76.90	$76.90
Purchase #2	$223.85	6.448%	$238.2838	$238.28	$238.30	$238.30
Purchase #3	$238.82	12.709%	$269.1716	$269.17	$269.15	$269.20
Purchase #4	$183.43	3.748%	$190.305	$190.31	$190.30	$190.30
Purchase #5	$48.58	8.690%	$52.8016	$52.80	$52.80	$52.80
Purchase #6	$208.38	7.445%	$223.8939	$223.89	$223.90	$223.90
Purchase #7	$124.25	6.271%	$132.0417	$132.04	$132.05	$132.00
7 purchase totals =	$1,095.17		$1,183.3843	$1,183.38	$1,183.40	$1,183.40