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	$85.79	5.268%	$90.3094	$90.31	$90.30	$90.30
Purchase #2	$220.84	13.133%	$249.8429	$249.84	$249.85	$249.80
Purchase #3	$98.38	12.407%	$110.586	$110.59	$110.60	$110.60
Purchase #4	$121.28	5.129%	$127.5005	$127.50	$127.50	$127.50
Purchase #5	$101.88	3.179%	$105.1188	$105.12	$105.10	$105.10
Purchase #6	$29.43	8.339%	$31.8842	$31.88	$31.90	$31.90
Purchase #7	$230.46	4.721%	$241.34	$241.34	$241.35	$241.30
7 purchase totals =	$888.06		$956.5818	$956.58	$956.60	$956.50