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	$146.58	12.389%	$164.7398	$164.74	$164.75	$164.70
Purchase #2	$86.77	4.867%	$90.9931	$90.99	$91.00	$91.00
Purchase #3	$178.96	3.638%	$185.4706	$185.47	$185.45	$185.50
Purchase #4	$119.77	12.147%	$134.3185	$134.32	$134.30	$134.30
Purchase #5	$31.74	9.194%	$34.6582	$34.66	$34.65	$34.70
Purchase #6	$113.43	8.651%	$123.2428	$123.24	$123.25	$123.20
Purchase #7	$54.31	4.108%	$56.5411	$56.54	$56.55	$56.50
7 purchase totals =	$731.56		$789.9641	$789.96	$789.95	$789.90