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	$47.76	5.604%	$50.4365	$50.44	$50.45	$50.40
Purchase #2	$89.89	11.844%	$100.5366	$100.54	$100.55	$100.50
Purchase #3	$241.60	13.531%	$274.2909	$274.29	$274.30	$274.30
Purchase #4	$45.76	7.560%	$49.2195	$49.22	$49.20	$49.20
Purchase #5	$219.87	11.601%	$245.3771	$245.38	$245.40	$245.40
Purchase #6	$31.36	10.429%	$34.6305	$34.63	$34.65	$34.60
Purchase #7	$85.57	3.471%	$88.5401	$88.54	$88.55	$88.50
7 purchase totals =	$761.81		$843.0312	$843.04	$843.10	$842.90