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	$133.93	4.103%	$139.4251	$139.43	$139.45	$139.40
Purchase #2	$172.77	10.333%	$190.6223	$190.62	$190.60	$190.60
Purchase #3	$141.78	7.675%	$152.6616	$152.66	$152.65	$152.70
Purchase #4	$72.52	11.340%	$80.7438	$80.74	$80.75	$80.70
Purchase #5	$211.80	9.769%	$232.4907	$232.49	$232.50	$232.50
Purchase #6	$54.56	9.707%	$59.8561	$59.86	$59.85	$59.90
Purchase #7	$19.45	7.511%	$20.9109	$20.91	$20.90	$20.90
7 purchase totals =	$806.81		$876.7105	$876.71	$876.70	$876.70