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	$52.26	7.542%	$56.2014	$56.20	$56.20	$56.20
Purchase #2	$99.80	4.156%	$103.9477	$103.95	$103.95	$103.90
Purchase #3	$80.50	11.178%	$89.4983	$89.50	$89.50	$89.50
Purchase #4	$163.56	3.221%	$168.8283	$168.83	$168.85	$168.80
Purchase #5	$6.39	11.742%	$7.1403	$7.14	$7.15	$7.10
Purchase #6	$122.77	8.869%	$133.6585	$133.66	$133.65	$133.70
Purchase #7	$136.80	11.231%	$152.164	$152.16	$152.15	$152.20
7 purchase totals =	$662.08		$711.4385	$711.44	$711.45	$711.40