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	$248.79	12.235%	$279.2295	$279.23	$279.25	$279.20
Purchase #2	$187.76	10.421%	$207.3265	$207.33	$207.35	$207.30
Purchase #3	$152.96	12.217%	$171.6471	$171.65	$171.65	$171.60
Purchase #4	$141.93	4.629%	$148.4999	$148.50	$148.50	$148.50
Purchase #5	$221.80	7.565%	$238.5792	$238.58	$238.60	$238.60
Purchase #6	$51.96	5.518%	$54.8272	$54.83	$54.85	$54.80
Purchase #7	$39.45	8.404%	$42.7654	$42.77	$42.75	$42.80
7 purchase totals =	$1,044.65		$1,142.8748	$1,142.89	$1,142.95	$1,142.80