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	$89.27	11.544%	$99.5753	$99.58	$99.60	$99.60
Purchase #2	$164.42	9.327%	$179.7555	$179.76	$179.75	$179.80
Purchase #3	$105.25	4.460%	$109.9442	$109.94	$109.95	$109.90
Purchase #4	$248.82	11.265%	$276.8496	$276.85	$276.85	$276.80
Purchase #5	$176.47	3.155%	$182.0376	$182.04	$182.05	$182.00
Purchase #6	$207.83	13.498%	$235.8829	$235.88	$235.90	$235.90
Purchase #7	$32.58	11.671%	$36.3824	$36.38	$36.40	$36.40
7 purchase totals =	$1,024.64		$1,120.4275	$1,120.43	$1,120.50	$1,120.40