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	$153.52	12.172%	$172.2065	$172.21	$172.20	$172.20
Purchase #2	$34.40	8.709%	$37.3959	$37.40	$37.40	$37.40
Purchase #3	$62.78	4.393%	$65.5379	$65.54	$65.55	$65.50
Purchase #4	$200.61	10.168%	$221.008	$221.01	$221.00	$221.00
Purchase #5	$27.95	4.819%	$29.2969	$29.30	$29.30	$29.30
Purchase #6	$66.31	4.576%	$69.3443	$69.34	$69.35	$69.30
Purchase #7	$124.71	12.762%	$140.6255	$140.63	$140.65	$140.60
7 purchase totals =	$670.28		$735.4150	$735.43	$735.45	$735.30