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	$164.92	3.330%	$170.4118	$170.41	$170.40	$170.40
Purchase #2	$109.98	8.765%	$119.6197	$119.62	$119.60	$119.60
Purchase #3	$46.82	9.491%	$51.2637	$51.26	$51.25	$51.30
Purchase #4	$6.57	4.743%	$6.8816	$6.88	$6.90	$6.90
Purchase #5	$54.96	4.617%	$57.4975	$57.50	$57.50	$57.50
Purchase #6	$182.95	4.256%	$190.7364	$190.74	$190.75	$190.70
Purchase #7	$72.89	13.675%	$82.8577	$82.86	$82.85	$82.90
7 purchase totals =	$639.09		$679.2684	$679.27	$679.25	$679.30