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	$37.44	4.118%	$38.9818	$38.98	$39.00	$39.00
Purchase #2	$115.68	11.102%	$128.5228	$128.52	$128.50	$128.50
Purchase #3	$225.86	10.865%	$250.3997	$250.40	$250.40	$250.40
Purchase #4	$161.58	5.766%	$170.8967	$170.90	$170.90	$170.90
Purchase #5	$163.52	4.262%	$170.4892	$170.49	$170.50	$170.50
Purchase #6	$106.97	4.432%	$111.7109	$111.71	$111.70	$111.70
Purchase #7	$92.68	6.736%	$98.9229	$98.92	$98.90	$98.90
7 purchase totals =	$903.73		$969.9240	$969.92	$969.90	$969.90