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	$47.82	7.657%	$51.4816	$51.48	$51.50	$51.50
Purchase #2	$126.94	10.562%	$140.3474	$140.35	$140.35	$140.30
Purchase #3	$249.69	7.493%	$268.3993	$268.40	$268.40	$268.40
Purchase #4	$232.86	5.320%	$245.2482	$245.25	$245.25	$245.20
Purchase #5	$100.84	10.527%	$111.4554	$111.46	$111.45	$111.50
Purchase #6	$107.88	9.735%	$118.3821	$118.38	$118.40	$118.40
Purchase #7	$143.68	4.804%	$150.5824	$150.58	$150.60	$150.60
7 purchase totals =	$1,009.71		$1,085.8964	$1,085.90	$1,085.95	$1,085.90