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	$11.51	6.265%	$12.2311	$12.23	$12.25	$12.20
Purchase #2	$26.65	3.164%	$27.4932	$27.49	$27.50	$27.50
Purchase #3	$142.96	3.848%	$148.4611	$148.46	$148.45	$148.50
Purchase #4	$191.79	4.856%	$201.1033	$201.10	$201.10	$201.10
Purchase #5	$37.48	7.631%	$40.3401	$40.34	$40.35	$40.30
Purchase #6	$7.43	3.494%	$7.6896	$7.69	$7.70	$7.70
Purchase #7	$82.70	9.172%	$90.2852	$90.29	$90.30	$90.30
7 purchase totals =	$500.52		$527.6036	$527.60	$527.65	$527.60