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	$250.30	9.685%	$274.5416	$274.54	$274.55	$274.50
Purchase #2	$115.29	10.847%	$127.7955	$127.80	$127.80	$127.80
Purchase #3	$104.89	4.558%	$109.6709	$109.67	$109.65	$109.70
Purchase #4	$116.86	13.230%	$132.3206	$132.32	$132.30	$132.30
Purchase #5	$163.78	11.529%	$182.6622	$182.66	$182.65	$182.70
Purchase #6	$101.72	3.659%	$105.4419	$105.44	$105.45	$105.40
Purchase #7	$8.60	3.185%	$8.8739	$8.87	$8.85	$8.90
7 purchase totals =	$861.44		$941.3066	$941.30	$941.25	$941.30