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	$62.40	6.106%	$66.2101	$66.21	$66.20	$66.20
Purchase #2	$221.31	11.433%	$246.6124	$246.61	$246.60	$246.60
Purchase #3	$211.30	13.781%	$240.4193	$240.42	$240.40	$240.40
Purchase #4	$85.54	8.672%	$92.958	$92.96	$92.95	$93.00
Purchase #5	$169.27	9.401%	$185.1831	$185.18	$185.20	$185.20
Purchase #6	$55.90	5.687%	$59.079	$59.08	$59.10	$59.10
Purchase #7	$134.39	10.723%	$148.8006	$148.80	$148.80	$148.80
7 purchase totals =	$940.11		$1,039.2625	$1,039.26	$1,039.25	$1,039.30