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	$79.43	6.566%	$84.6454	$84.65	$84.65	$84.60
Purchase #2	$52.49	12.603%	$59.1053	$59.11	$59.10	$59.10
Purchase #3	$192.31	4.267%	$200.5159	$200.52	$200.50	$200.50
Purchase #4	$148.68	10.826%	$164.7761	$164.78	$164.80	$164.80
Purchase #5	$32.40	3.152%	$33.4212	$33.42	$33.40	$33.40
Purchase #6	$73.69	10.738%	$81.6028	$81.60	$81.60	$81.60
Purchase #7	$243.57	9.404%	$266.4753	$266.48	$266.50	$266.50
7 purchase totals =	$822.57		$890.5420	$890.56	$890.55	$890.50