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	$80.69	8.384%	$87.455	$87.46	$87.45	$87.50
Purchase #2	$91.45	7.214%	$98.0472	$98.05	$98.05	$98.00
Purchase #3	$248.37	13.382%	$281.6069	$281.61	$281.60	$281.60
Purchase #4	$206.53	10.536%	$228.29	$228.29	$228.30	$228.30
Purchase #5	$217.53	10.596%	$240.5795	$240.58	$240.60	$240.60
Purchase #6	$33.71	12.309%	$37.8594	$37.86	$37.85	$37.90
Purchase #7	$144.38	12.645%	$162.6369	$162.64	$162.65	$162.60
7 purchase totals =	$1,022.66		$1,136.4749	$1,136.49	$1,136.50	$1,136.50