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	$249.93	7.456%	$268.5648	$268.56	$268.55	$268.60
Purchase #2	$102.51	12.671%	$115.499	$115.50	$115.50	$115.50
Purchase #3	$168.77	9.552%	$184.8909	$184.89	$184.90	$184.90
Purchase #4	$103.70	13.512%	$117.7119	$117.71	$117.70	$117.70
Purchase #5	$52.29	8.689%	$56.8335	$56.83	$56.85	$56.80
Purchase #6	$207.90	9.238%	$227.1058	$227.11	$227.10	$227.10
Purchase #7	$81.54	11.602%	$91.0003	$91.00	$91.00	$91.00
7 purchase totals =	$966.64		$1,061.6062	$1,061.60	$1,061.60	$1,061.60