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	$56.92	7.720%	$61.3142	$61.31	$61.30	$61.30
Purchase #2	$41.30	12.534%	$46.4765	$46.48	$46.50	$46.50
Purchase #3	$218.27	12.442%	$245.4272	$245.43	$245.45	$245.40
Purchase #4	$15.51	11.826%	$17.3442	$17.34	$17.35	$17.30
Purchase #5	$145.40	11.569%	$162.2213	$162.22	$162.20	$162.20
Purchase #6	$141.38	4.186%	$147.2982	$147.30	$147.30	$147.30
Purchase #7	$169.27	7.219%	$181.4896	$181.49	$181.50	$181.50
7 purchase totals =	$788.05		$861.5712	$861.57	$861.60	$861.50