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	$78.60	3.680%	$81.4925	$81.49	$81.50	$81.50
Purchase #2	$163.38	10.395%	$180.3634	$180.36	$180.35	$180.40
Purchase #3	$128.46	10.356%	$141.7633	$141.76	$141.75	$141.80
Purchase #4	$39.75	9.695%	$43.6038	$43.60	$43.60	$43.60
Purchase #5	$241.40	13.731%	$274.5466	$274.55	$274.55	$274.50
Purchase #6	$178.71	11.257%	$198.8274	$198.83	$198.85	$198.80
Purchase #7	$145.89	8.261%	$157.942	$157.94	$157.95	$157.90
7 purchase totals =	$976.19		$1,078.5390	$1,078.53	$1,078.55	$1,078.50