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	$214.25	11.402%	$238.6788	$238.68	$238.70	$238.70
Purchase #2	$66.66	12.154%	$74.7619	$74.76	$74.75	$74.80
Purchase #3	$89.34	12.820%	$100.7934	$100.79	$100.80	$100.80
Purchase #4	$171.51	7.839%	$184.9547	$184.95	$184.95	$185.00
Purchase #5	$5.31	4.462%	$5.5469	$5.55	$5.55	$5.50
Purchase #6	$88.86	10.724%	$98.3893	$98.39	$98.40	$98.40
Purchase #7	$82.85	7.250%	$88.8566	$88.86	$88.85	$88.90
7 purchase totals =	$718.78		$791.9816	$791.98	$792.00	$792.10