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	$37.60	8.780%	$40.9013	$40.90	$40.90	$40.90
Purchase #2	$82.42	6.687%	$87.9314	$87.93	$87.95	$87.90
Purchase #3	$94.55	4.138%	$98.4625	$98.46	$98.45	$98.50
Purchase #4	$224.45	13.236%	$254.1582	$254.16	$254.15	$254.20
Purchase #5	$118.46	6.784%	$126.4963	$126.50	$126.50	$126.50
Purchase #6	$140.38	5.679%	$148.3522	$148.35	$148.35	$148.40
Purchase #7	$33.89	10.641%	$37.4962	$37.50	$37.50	$37.50
7 purchase totals =	$731.75		$793.7981	$793.80	$793.80	$793.90