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	$109.54	8.500%	$118.8509	$118.85	$118.85	$118.90
Purchase #2	$144.28	13.820%	$164.2195	$164.22	$164.20	$164.20
Purchase #3	$183.69	11.536%	$204.8805	$204.88	$204.90	$204.90
Purchase #4	$243.40	10.627%	$269.2661	$269.27	$269.25	$269.30
Purchase #5	$102.43	3.439%	$105.9526	$105.95	$105.95	$106.00
Purchase #6	$99.82	12.543%	$112.3404	$112.34	$112.35	$112.30
Purchase #7	$6.90	10.103%	$7.5971	$7.60	$7.60	$7.60
7 purchase totals =	$890.06		$983.1071	$983.11	$983.10	$983.20