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	$50.38	3.452%	$52.1191	$52.12	$52.10	$52.10
Purchase #2	$237.72	5.113%	$249.8746	$249.87	$249.85	$249.90
Purchase #3	$51.28	13.734%	$58.3228	$58.32	$58.30	$58.30
Purchase #4	$107.39	5.776%	$113.5928	$113.59	$113.60	$113.60
Purchase #5	$159.85	7.741%	$172.224	$172.22	$172.20	$172.20
Purchase #6	$33.71	3.129%	$34.7648	$34.76	$34.75	$34.80
Purchase #7	$181.99	8.151%	$196.824	$196.82	$196.80	$196.80
7 purchase totals =	$822.32		$877.7221	$877.70	$877.60	$877.70