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	$123.52	10.790%	$136.8478	$136.85	$136.85	$136.80
Purchase #2	$165.32	13.103%	$186.9819	$186.98	$187.00	$187.00
Purchase #3	$159.34	9.462%	$174.4168	$174.42	$174.40	$174.40
Purchase #4	$28.46	3.304%	$29.4003	$29.40	$29.40	$29.40
Purchase #5	$102.57	8.320%	$111.1038	$111.10	$111.10	$111.10
Purchase #6	$196.88	12.618%	$221.7223	$221.72	$221.70	$221.70
Purchase #7	$46.55	11.373%	$51.8441	$51.84	$51.85	$51.80
7 purchase totals =	$822.64		$912.3170	$912.31	$912.30	$912.20