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	$87.64	7.124%	$93.8835	$93.88	$93.90	$93.90
Purchase #2	$151.91	4.305%	$158.4497	$158.45	$158.45	$158.40
Purchase #3	$157.72	11.450%	$175.7789	$175.78	$175.80	$175.80
Purchase #4	$78.60	8.539%	$85.3117	$85.31	$85.30	$85.30
Purchase #5	$92.66	10.593%	$102.4755	$102.48	$102.50	$102.50
Purchase #6	$126.94	13.298%	$143.8205	$143.82	$143.80	$143.80
Purchase #7	$83.25	10.112%	$91.6682	$91.67	$91.65	$91.70
7 purchase totals =	$778.72		$851.3880	$851.39	$851.40	$851.40