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	$153.80	12.334%	$172.7697	$172.77	$172.75	$172.80
Purchase #2	$118.36	11.391%	$131.8424	$131.84	$131.85	$131.80
Purchase #3	$172.75	12.109%	$193.6683	$193.67	$193.65	$193.70
Purchase #4	$34.84	9.120%	$38.0174	$38.02	$38.00	$38.00
Purchase #5	$97.90	9.703%	$107.3992	$107.40	$107.40	$107.40
Purchase #6	$95.31	5.473%	$100.5263	$100.53	$100.55	$100.50
Purchase #7	$40.30	12.304%	$45.2585	$45.26	$45.25	$45.30
7 purchase totals =	$713.26		$789.4818	$789.49	$789.45	$789.50