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	$26.51	11.700%	$29.6117	$29.61	$29.60	$29.60
Purchase #2	$161.53	3.696%	$167.5001	$167.50	$167.50	$167.50
Purchase #3	$104.43	4.669%	$109.3058	$109.31	$109.30	$109.30
Purchase #4	$237.55	4.695%	$248.703	$248.70	$248.70	$248.70
Purchase #5	$183.69	12.492%	$206.6366	$206.64	$206.65	$206.60
Purchase #6	$150.74	11.792%	$168.5153	$168.52	$168.50	$168.50
Purchase #7	$51.71	5.422%	$54.5137	$54.51	$54.50	$54.50
7 purchase totals =	$916.16		$984.7862	$984.79	$984.75	$984.70