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	$21.53	12.439%	$24.2081	$24.21	$24.20	$24.20
Purchase #2	$221.90	3.166%	$228.9254	$228.93	$228.95	$228.90
Purchase #3	$224.97	11.305%	$250.4029	$250.40	$250.40	$250.40
Purchase #4	$99.60	13.210%	$112.7572	$112.76	$112.75	$112.80
Purchase #5	$211.27	8.187%	$228.5667	$228.57	$228.55	$228.60
Purchase #6	$82.62	9.500%	$90.4689	$90.47	$90.45	$90.50
Purchase #7	$92.27	12.251%	$103.574	$103.57	$103.55	$103.60
7 purchase totals =	$954.16		$1,038.9032	$1,038.91	$1,038.85	$1,039.00