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	$24.32	10.559%	$26.8879	$26.89	$26.90	$26.90
Purchase #2	$72.31	8.262%	$78.2843	$78.28	$78.30	$78.30
Purchase #3	$103.66	3.547%	$107.3368	$107.34	$107.35	$107.30
Purchase #4	$84.50	8.229%	$91.4535	$91.45	$91.45	$91.50
Purchase #5	$206.69	3.103%	$213.1036	$213.10	$213.10	$213.10
Purchase #6	$51.47	12.249%	$57.7746	$57.77	$57.75	$57.80
Purchase #7	$39.91	6.785%	$42.6179	$42.62	$42.60	$42.60
7 purchase totals =	$582.86		$617.4586	$617.45	$617.45	$617.50