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	$94.59	9.337%	$103.4219	$103.42	$103.40	$103.40
Purchase #2	$227.45	10.326%	$250.9365	$250.94	$250.95	$250.90
Purchase #3	$228.53	5.751%	$241.6728	$241.67	$241.65	$241.70
Purchase #4	$57.59	3.619%	$59.6742	$59.67	$59.65	$59.70
Purchase #5	$7.99	5.419%	$8.423	$8.42	$8.40	$8.40
Purchase #6	$40.77	4.210%	$42.4864	$42.49	$42.50	$42.50
Purchase #7	$85.64	7.768%	$92.2925	$92.29	$92.30	$92.30
7 purchase totals =	$742.56		$798.9073	$798.90	$798.85	$798.90