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	$107.85	3.284%	$111.3918	$111.39	$111.40	$111.40
Purchase #2	$154.27	12.222%	$173.1249	$173.12	$173.10	$173.10
Purchase #3	$82.53	10.373%	$91.0908	$91.09	$91.10	$91.10
Purchase #4	$217.35	11.655%	$242.6821	$242.68	$242.70	$242.70
Purchase #5	$55.40	13.527%	$62.894	$62.89	$62.90	$62.90
Purchase #6	$63.41	6.696%	$67.6559	$67.66	$67.65	$67.70
Purchase #7	$146.56	10.587%	$162.0763	$162.08	$162.10	$162.10
7 purchase totals =	$827.37		$910.9158	$910.91	$910.95	$911.00