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	$99.54	9.305%	$108.8022	$108.80	$108.80	$108.80
Purchase #2	$222.61	12.476%	$250.3828	$250.38	$250.40	$250.40
Purchase #3	$51.73	12.825%	$58.3644	$58.36	$58.35	$58.40
Purchase #4	$12.85	5.404%	$13.5444	$13.54	$13.55	$13.50
Purchase #5	$234.39	9.281%	$256.1437	$256.14	$256.15	$256.10
Purchase #6	$37.82	10.855%	$41.9254	$41.93	$41.95	$41.90
Purchase #7	$59.63	4.237%	$62.1565	$62.16	$62.15	$62.20
7 purchase totals =	$718.57		$791.3194	$791.31	$791.35	$791.30