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	$248.70	13.234%	$281.613	$281.61	$281.60	$281.60
Purchase #2	$242.46	6.730%	$258.7776	$258.78	$258.80	$258.80
Purchase #3	$152.43	13.213%	$172.5706	$172.57	$172.55	$172.60
Purchase #4	$145.69	11.203%	$162.0117	$162.01	$162.00	$162.00
Purchase #5	$16.52	13.290%	$18.7155	$18.72	$18.70	$18.70
Purchase #6	$52.51	4.662%	$54.958	$54.96	$54.95	$55.00
Purchase #7	$200.35	7.485%	$215.3462	$215.35	$215.35	$215.30
7 purchase totals =	$1,058.66		$1,163.9926	$1,164.00	$1,163.95	$1,164.00