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	$160.89	11.383%	$179.2041	$179.20	$179.20	$179.20
Purchase #2	$122.58	4.305%	$127.8571	$127.86	$127.85	$127.90
Purchase #3	$65.37	8.470%	$70.9068	$70.91	$70.90	$70.90
Purchase #4	$151.60	8.498%	$164.483	$164.48	$164.50	$164.50
Purchase #5	$22.81	4.401%	$23.8139	$23.81	$23.80	$23.80
Purchase #6	$95.57	6.360%	$101.6483	$101.65	$101.65	$101.60
Purchase #7	$37.32	9.676%	$40.9311	$40.93	$40.95	$40.90
7 purchase totals =	$656.14		$708.8443	$708.84	$708.85	$708.80