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	$29.98	5.597%	$31.658	$31.66	$31.65	$31.70
Purchase #2	$217.52	9.466%	$238.1104	$238.11	$238.10	$238.10
Purchase #3	$196.83	11.702%	$219.863	$219.86	$219.85	$219.90
Purchase #4	$59.33	13.837%	$67.5395	$67.54	$67.55	$67.50
Purchase #5	$129.68	8.796%	$141.0867	$141.09	$141.10	$141.10
Purchase #6	$124.42	12.632%	$140.1367	$140.14	$140.15	$140.10
Purchase #7	$21.75	11.336%	$24.2156	$24.22	$24.20	$24.20
7 purchase totals =	$779.51		$862.6099	$862.62	$862.60	$862.60