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	$15.48	11.440%	$17.2509	$17.25	$17.25	$17.30
Purchase #2	$210.89	13.577%	$239.5225	$239.52	$239.50	$239.50
Purchase #3	$100.63	3.102%	$103.7515	$103.75	$103.75	$103.80
Purchase #4	$94.37	5.417%	$99.482	$99.48	$99.50	$99.50
Purchase #5	$25.91	13.495%	$29.4066	$29.41	$29.40	$29.40
Purchase #6	$145.59	10.463%	$160.8231	$160.82	$160.80	$160.80
Purchase #7	$225.37	7.340%	$241.9122	$241.91	$241.90	$241.90
7 purchase totals =	$818.24		$892.1488	$892.14	$892.10	$892.20