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	$82.97	11.593%	$92.5887	$92.59	$92.60	$92.60
Purchase #2	$69.85	9.249%	$76.3104	$76.31	$76.30	$76.30
Purchase #3	$162.92	13.817%	$185.4307	$185.43	$185.45	$185.40
Purchase #4	$229.55	12.630%	$258.5422	$258.54	$258.55	$258.50
Purchase #5	$107.45	3.382%	$111.084	$111.08	$111.10	$111.10
Purchase #6	$212.74	12.476%	$239.2814	$239.28	$239.30	$239.30
Purchase #7	$71.78	5.722%	$75.8873	$75.89	$75.90	$75.90
7 purchase totals =	$937.26		$1,039.1247	$1,039.12	$1,039.20	$1,039.10