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	$100.79	7.548%	$108.3976	$108.40	$108.40	$108.40
Purchase #2	$158.28	4.546%	$165.4754	$165.48	$165.50	$165.50
Purchase #3	$119.73	8.453%	$129.8508	$129.85	$129.85	$129.90
Purchase #4	$100.46	9.127%	$109.629	$109.63	$109.65	$109.60
Purchase #5	$100.91	8.874%	$109.8648	$109.86	$109.85	$109.90
Purchase #6	$83.54	11.184%	$92.8831	$92.88	$92.90	$92.90
Purchase #7	$214.49	12.352%	$240.9838	$240.98	$241.00	$241.00
7 purchase totals =	$878.20		$957.0845	$957.08	$957.15	$957.20