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	$153.67	12.691%	$173.1723	$173.17	$173.15	$173.20
Purchase #2	$195.32	10.591%	$216.0063	$216.01	$216.00	$216.00
Purchase #3	$36.25	7.245%	$38.8763	$38.88	$38.90	$38.90
Purchase #4	$201.77	9.274%	$220.4821	$220.48	$220.50	$220.50
Purchase #5	$150.54	5.264%	$158.4644	$158.46	$158.45	$158.50
Purchase #6	$29.80	12.669%	$33.5754	$33.58	$33.60	$33.60
Purchase #7	$9.37	11.855%	$10.4808	$10.48	$10.50	$10.50
7 purchase totals =	$776.72		$851.0576	$851.06	$851.10	$851.20