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	$39.84	7.250%	$42.7284	$42.73	$42.75	$42.70
Purchase #2	$207.62	6.873%	$221.8897	$221.89	$221.90	$221.90
Purchase #3	$40.45	12.212%	$45.3898	$45.39	$45.40	$45.40
Purchase #4	$221.67	4.176%	$230.9269	$230.93	$230.95	$230.90
Purchase #5	$40.77	3.693%	$42.2756	$42.28	$42.30	$42.30
Purchase #6	$140.99	9.439%	$154.298	$154.30	$154.30	$154.30
Purchase #7	$205.48	9.767%	$225.5492	$225.55	$225.55	$225.50
7 purchase totals =	$896.82		$963.0576	$963.07	$963.15	$963.00