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	$139.94	3.262%	$144.5048	$144.50	$144.50	$144.50
Purchase #2	$144.30	6.184%	$153.2235	$153.22	$153.20	$153.20
Purchase #3	$96.74	3.657%	$100.2778	$100.28	$100.30	$100.30
Purchase #4	$169.58	9.384%	$185.4934	$185.49	$185.50	$185.50
Purchase #5	$94.85	10.683%	$104.9828	$104.98	$105.00	$105.00
Purchase #6	$18.90	9.566%	$20.708	$20.71	$20.70	$20.70
Purchase #7	$81.80	13.159%	$92.5641	$92.56	$92.55	$92.60
7 purchase totals =	$746.11		$801.7544	$801.74	$801.75	$801.80