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	$213.36	13.152%	$241.4211	$241.42	$241.40	$241.40
Purchase #2	$54.45	10.294%	$60.0551	$60.06	$60.05	$60.10
Purchase #3	$67.91	13.735%	$77.2374	$77.24	$77.25	$77.20
Purchase #4	$236.55	12.128%	$265.2388	$265.24	$265.25	$265.20
Purchase #5	$222.34	4.142%	$231.5493	$231.55	$231.55	$231.50
Purchase #6	$73.73	6.600%	$78.5962	$78.60	$78.60	$78.60
Purchase #7	$36.79	4.331%	$38.3834	$38.38	$38.40	$38.40
7 purchase totals =	$905.13		$992.4813	$992.49	$992.50	$992.40