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	$248.80	9.132%	$271.5204	$271.52	$271.50	$271.50
Purchase #2	$134.74	6.697%	$143.7635	$143.76	$143.75	$143.80
Purchase #3	$106.91	5.613%	$112.9109	$112.91	$112.90	$112.90
Purchase #4	$143.62	10.169%	$158.2247	$158.22	$158.20	$158.20
Purchase #5	$52.84	12.841%	$59.6252	$59.63	$59.65	$59.60
Purchase #6	$20.69	4.513%	$21.6237	$21.62	$21.60	$21.60
Purchase #7	$240.54	9.292%	$262.891	$262.89	$262.90	$262.90
7 purchase totals =	$948.14		$1,030.5594	$1,030.55	$1,030.50	$1,030.50