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	$175.97	5.154%	$185.0395	$185.04	$185.05	$185.00
Purchase #2	$133.90	9.334%	$146.3982	$146.40	$146.40	$146.40
Purchase #3	$183.27	7.316%	$196.678	$196.68	$196.70	$196.70
Purchase #4	$9.87	13.159%	$11.1688	$11.17	$11.15	$11.20
Purchase #5	$40.27	3.334%	$41.6126	$41.61	$41.60	$41.60
Purchase #6	$52.41	3.617%	$54.3057	$54.31	$54.30	$54.30
Purchase #7	$17.49	10.867%	$19.3906	$19.39	$19.40	$19.40
7 purchase totals =	$613.18		$654.5934	$654.60	$654.60	$654.60