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	$102.28	12.808%	$115.38	$115.38	$115.40	$115.40
Purchase #2	$250.71	3.649%	$259.8584	$259.86	$259.85	$259.90
Purchase #3	$16.47	13.384%	$18.6743	$18.67	$18.65	$18.70
Purchase #4	$95.91	4.180%	$99.919	$99.92	$99.90	$99.90
Purchase #5	$151.79	13.648%	$172.5063	$172.51	$172.50	$172.50
Purchase #6	$26.76	10.181%	$29.4844	$29.48	$29.50	$29.50
Purchase #7	$118.26	8.791%	$128.6562	$128.66	$128.65	$128.70
7 purchase totals =	$762.18		$824.4786	$824.48	$824.45	$824.60