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	$131.25	6.372%	$139.6133	$139.61	$139.60	$139.60
Purchase #2	$209.43	3.871%	$217.537	$217.54	$217.55	$217.50
Purchase #3	$240.94	3.460%	$249.2765	$249.28	$249.30	$249.30
Purchase #4	$181.48	3.122%	$187.1458	$187.15	$187.15	$187.10
Purchase #5	$145.42	4.310%	$151.6876	$151.69	$151.70	$151.70
Purchase #6	$220.33	11.275%	$245.1722	$245.17	$245.15	$245.20
Purchase #7	$138.27	7.721%	$148.9458	$148.95	$148.95	$148.90
7 purchase totals =	$1,267.12		$1,339.3782	$1,339.39	$1,339.40	$1,339.30