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	$177.39	7.450%	$190.6056	$190.61	$190.60	$190.60
Purchase #2	$101.66	9.395%	$111.211	$111.21	$111.20	$111.20
Purchase #3	$157.67	8.466%	$171.0183	$171.02	$171.00	$171.00
Purchase #4	$50.89	3.530%	$52.6864	$52.69	$52.70	$52.70
Purchase #5	$41.63	9.636%	$45.6415	$45.64	$45.65	$45.60
Purchase #6	$171.33	11.347%	$190.7708	$190.77	$190.75	$190.80
Purchase #7	$33.93	10.150%	$37.3739	$37.37	$37.35	$37.40
7 purchase totals =	$734.50		$799.3075	$799.31	$799.25	$799.30