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	$241.42	3.791%	$250.5722	$250.57	$250.55	$250.60
Purchase #2	$138.81	8.597%	$150.7435	$150.74	$150.75	$150.70
Purchase #3	$57.98	8.182%	$62.7239	$62.72	$62.70	$62.70
Purchase #4	$97.78	13.832%	$111.3049	$111.30	$111.30	$111.30
Purchase #5	$22.95	7.401%	$24.6485	$24.65	$24.65	$24.60
Purchase #6	$42.78	10.112%	$47.1059	$47.11	$47.10	$47.10
Purchase #7	$104.36	6.778%	$111.4335	$111.43	$111.45	$111.40
7 purchase totals =	$706.08		$758.5324	$758.52	$758.50	$758.40