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	$25.32	7.811%	$27.2977	$27.30	$27.30	$27.30
Purchase #2	$246.73	4.836%	$258.6619	$258.66	$258.65	$258.70
Purchase #3	$228.25	4.508%	$238.5395	$238.54	$238.55	$238.50
Purchase #4	$150.86	5.107%	$158.5644	$158.56	$158.55	$158.60
Purchase #5	$174.81	12.210%	$196.1543	$196.15	$196.15	$196.20
Purchase #6	$140.33	7.732%	$151.1803	$151.18	$151.20	$151.20
Purchase #7	$146.47	10.572%	$161.9548	$161.95	$161.95	$162.00
7 purchase totals =	$1,112.77		$1,192.3529	$1,192.34	$1,192.35	$1,192.50