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	$162.82	8.114%	$176.0312	$176.03	$176.05	$176.00
Purchase #2	$126.86	11.429%	$141.3588	$141.36	$141.35	$141.40
Purchase #3	$79.40	11.698%	$88.6882	$88.69	$88.70	$88.70
Purchase #4	$150.70	13.532%	$171.0927	$171.09	$171.10	$171.10
Purchase #5	$40.37	6.260%	$42.8972	$42.90	$42.90	$42.90
Purchase #6	$50.58	5.408%	$53.3154	$53.32	$53.30	$53.30
Purchase #7	$221.41	7.593%	$238.2217	$238.22	$238.20	$238.20
7 purchase totals =	$832.14		$911.6052	$911.61	$911.60	$911.60