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	$184.82	6.436%	$196.715	$196.72	$196.70	$196.70
Purchase #2	$117.88	7.452%	$126.6644	$126.66	$126.65	$126.70
Purchase #3	$139.98	8.524%	$151.9119	$151.91	$151.90	$151.90
Purchase #4	$231.42	3.766%	$240.1353	$240.14	$240.15	$240.10
Purchase #5	$175.31	3.261%	$181.0269	$181.03	$181.05	$181.00
Purchase #6	$73.64	10.545%	$81.4053	$81.41	$81.40	$81.40
Purchase #7	$18.47	8.520%	$20.0436	$20.04	$20.05	$20.00
7 purchase totals =	$941.52		$997.9024	$997.91	$997.90	$997.80