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	$24.77	4.517%	$25.8889	$25.89	$25.90	$25.90
Purchase #2	$56.67	6.103%	$60.1286	$60.13	$60.15	$60.10
Purchase #3	$173.56	8.806%	$188.8437	$188.84	$188.85	$188.80
Purchase #4	$215.50	9.539%	$236.0565	$236.06	$236.05	$236.10
Purchase #5	$233.38	11.357%	$259.885	$259.89	$259.90	$259.90
Purchase #6	$109.65	12.298%	$123.1348	$123.13	$123.15	$123.10
Purchase #7	$129.28	11.675%	$144.3734	$144.37	$144.35	$144.40
7 purchase totals =	$942.81		$1,038.3109	$1,038.31	$1,038.35	$1,038.30