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	$134.66	4.491%	$140.7076	$140.71	$140.70	$140.70
Purchase #2	$96.34	7.124%	$103.2033	$103.20	$103.20	$103.20
Purchase #3	$34.54	5.781%	$36.5368	$36.54	$36.55	$36.50
Purchase #4	$163.47	11.245%	$181.8522	$181.85	$181.85	$181.90
Purchase #5	$51.39	7.680%	$55.3368	$55.34	$55.35	$55.30
Purchase #6	$84.28	9.291%	$92.1105	$92.11	$92.10	$92.10
Purchase #7	$51.72	11.427%	$57.63	$57.63	$57.65	$57.60
7 purchase totals =	$616.40		$667.3772	$667.38	$667.40	$667.30