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	$113.70	6.375%	$120.9484	$120.95	$120.95	$120.90
Purchase #2	$8.87	5.548%	$9.3621	$9.36	$9.35	$9.40
Purchase #3	$226.37	13.235%	$256.3301	$256.33	$256.35	$256.30
Purchase #4	$241.35	13.726%	$274.4777	$274.48	$274.50	$274.50
Purchase #5	$121.88	7.792%	$131.3769	$131.38	$131.40	$131.40
Purchase #6	$81.40	6.362%	$86.5787	$86.58	$86.60	$86.60
Purchase #7	$82.31	9.833%	$90.4035	$90.40	$90.40	$90.40
7 purchase totals =	$875.88		$969.4774	$969.48	$969.55	$969.50