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	$233.98	5.324%	$246.4371	$246.44	$246.45	$246.40
Purchase #2	$27.53	3.137%	$28.3936	$28.39	$28.40	$28.40
Purchase #3	$148.89	6.641%	$158.7778	$158.78	$158.80	$158.80
Purchase #4	$105.48	4.637%	$110.3711	$110.37	$110.35	$110.40
Purchase #5	$41.41	8.456%	$44.9116	$44.91	$44.90	$44.90
Purchase #6	$69.58	12.602%	$78.3485	$78.35	$78.35	$78.30
Purchase #7	$20.25	5.342%	$21.3318	$21.33	$21.35	$21.30
7 purchase totals =	$647.12		$688.5715	$688.57	$688.60	$688.50