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	$153.43	12.762%	$173.0107	$173.01	$173.00	$173.00
Purchase #2	$242.55	3.300%	$250.5542	$250.55	$250.55	$250.60
Purchase #3	$70.90	7.805%	$76.4337	$76.43	$76.45	$76.40
Purchase #4	$25.64	11.368%	$28.5548	$28.55	$28.55	$28.60
Purchase #5	$99.76	11.843%	$111.5746	$111.57	$111.55	$111.60
Purchase #6	$61.76	9.169%	$67.4228	$67.42	$67.40	$67.40
Purchase #7	$245.87	10.736%	$272.2666	$272.27	$272.25	$272.30
7 purchase totals =	$899.91		$979.8174	$979.80	$979.75	$979.90