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	$89.40	8.144%	$96.6807	$96.68	$96.70	$96.70
Purchase #2	$54.53	9.411%	$59.6618	$59.66	$59.65	$59.70
Purchase #3	$141.30	9.288%	$154.4239	$154.42	$154.40	$154.40
Purchase #4	$47.88	11.255%	$53.2689	$53.27	$53.25	$53.30
Purchase #5	$59.89	3.342%	$61.8915	$61.89	$61.90	$61.90
Purchase #6	$219.50	12.416%	$246.7531	$246.75	$246.75	$246.80
Purchase #7	$227.49	5.684%	$240.4205	$240.42	$240.40	$240.40
7 purchase totals =	$839.99		$913.1004	$913.09	$913.05	$913.20