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	$37.78	8.145%	$40.8572	$40.86	$40.85	$40.90
Purchase #2	$36.89	6.785%	$39.393	$39.39	$39.40	$39.40
Purchase #3	$93.30	9.456%	$102.1224	$102.12	$102.10	$102.10
Purchase #4	$124.77	12.324%	$140.1467	$140.15	$140.15	$140.10
Purchase #5	$234.28	9.622%	$256.8224	$256.82	$256.80	$256.80
Purchase #6	$164.53	11.852%	$184.0301	$184.03	$184.05	$184.00
Purchase #7	$228.27	8.812%	$248.3852	$248.39	$248.40	$248.40
7 purchase totals =	$919.82		$1,011.7570	$1,011.76	$1,011.75	$1,011.70