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	$230.27	3.426%	$238.1591	$238.16	$238.15	$238.20
Purchase #2	$29.79	5.390%	$31.3957	$31.40	$31.40	$31.40
Purchase #3	$147.57	3.273%	$152.4	$152.40	$152.40	$152.40
Purchase #4	$29.45	9.361%	$32.2068	$32.21	$32.20	$32.20
Purchase #5	$95.78	4.495%	$100.0853	$100.09	$100.10	$100.10
Purchase #6	$125.74	4.656%	$131.5945	$131.59	$131.60	$131.60
Purchase #7	$136.80	7.429%	$146.9629	$146.96	$146.95	$147.00
7 purchase totals =	$795.40		$832.8043	$832.81	$832.80	$832.90