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	$210.85	12.393%	$236.9806	$236.98	$237.00	$237.00
Purchase #2	$214.56	11.219%	$238.6315	$238.63	$238.65	$238.60
Purchase #3	$48.60	11.151%	$54.0194	$54.02	$54.00	$54.00
Purchase #4	$93.25	8.643%	$101.3096	$101.31	$101.30	$101.30
Purchase #5	$107.26	8.672%	$116.5616	$116.56	$116.55	$116.60
Purchase #6	$71.28	10.147%	$78.5128	$78.51	$78.50	$78.50
Purchase #7	$147.32	12.595%	$165.875	$165.88	$165.90	$165.90
7 purchase totals =	$893.12		$991.8905	$991.89	$991.90	$991.90