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	$219.53	10.655%	$242.9209	$242.92	$242.90	$242.90
Purchase #2	$33.97	9.143%	$37.0759	$37.08	$37.10	$37.10
Purchase #3	$177.93	6.734%	$189.9118	$189.91	$189.90	$189.90
Purchase #4	$246.39	12.411%	$276.9695	$276.97	$276.95	$277.00
Purchase #5	$102.98	8.287%	$111.514	$111.51	$111.50	$111.50
Purchase #6	$231.82	13.136%	$262.2719	$262.27	$262.25	$262.30
Purchase #7	$159.25	13.663%	$181.0083	$181.01	$181.00	$181.00
7 purchase totals =	$1,171.87		$1,301.6723	$1,301.67	$1,301.60	$1,301.70