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	$85.82	5.665%	$90.6817	$90.68	$90.70	$90.70
Purchase #2	$132.79	10.783%	$147.1087	$147.11	$147.10	$147.10
Purchase #3	$84.90	5.199%	$89.314	$89.31	$89.30	$89.30
Purchase #4	$237.68	13.845%	$270.5868	$270.59	$270.60	$270.60
Purchase #5	$12.63	3.183%	$13.032	$13.03	$13.05	$13.00
Purchase #6	$45.92	10.697%	$50.8321	$50.83	$50.85	$50.80
Purchase #7	$161.87	5.764%	$171.2002	$171.20	$171.20	$171.20
7 purchase totals =	$761.61		$832.7555	$832.75	$832.80	$832.70