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	$80.62	11.635%	$90.0001	$90.00	$90.00	$90.00
Purchase #2	$35.96	7.604%	$38.6944	$38.69	$38.70	$38.70
Purchase #3	$62.54	8.431%	$67.8127	$67.81	$67.80	$67.80
Purchase #4	$187.63	6.652%	$200.1111	$200.11	$200.10	$200.10
Purchase #5	$158.38	11.332%	$176.3276	$176.33	$176.35	$176.30
Purchase #6	$61.97	9.244%	$67.6985	$67.70	$67.70	$67.70
Purchase #7	$153.43	8.306%	$166.1739	$166.17	$166.15	$166.20
7 purchase totals =	$740.53		$806.8183	$806.81	$806.80	$806.80