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	$237.64	11.861%	$265.8265	$265.83	$265.85	$265.80
Purchase #2	$53.65	11.495%	$59.8171	$59.82	$59.80	$59.80
Purchase #3	$242.56	13.365%	$274.9781	$274.98	$275.00	$275.00
Purchase #4	$113.60	9.748%	$124.6737	$124.67	$124.65	$124.70
Purchase #5	$212.34	11.789%	$237.3728	$237.37	$237.35	$237.40
Purchase #6	$228.90	5.324%	$241.0866	$241.09	$241.10	$241.10
Purchase #7	$63.33	7.114%	$67.8353	$67.84	$67.85	$67.80
7 purchase totals =	$1,152.02		$1,271.5901	$1,271.60	$1,271.60	$1,271.60