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	$8.47	12.453%	$9.5248	$9.52	$9.50	$9.50
Purchase #2	$152.81	5.659%	$161.4575	$161.46	$161.45	$161.50
Purchase #3	$68.78	3.843%	$71.4232	$71.42	$71.40	$71.40
Purchase #4	$135.32	5.272%	$142.4541	$142.45	$142.45	$142.50
Purchase #5	$35.46	10.504%	$39.1847	$39.18	$39.20	$39.20
Purchase #6	$159.90	8.298%	$173.1685	$173.17	$173.15	$173.20
Purchase #7	$46.43	11.204%	$51.632	$51.63	$51.65	$51.60
7 purchase totals =	$607.17		$648.8448	$648.83	$648.80	$648.90