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	$129.36	11.542%	$144.2907	$144.29	$144.30	$144.30
Purchase #2	$168.52	7.442%	$181.0613	$181.06	$181.05	$181.10
Purchase #3	$230.83	10.770%	$255.6904	$255.69	$255.70	$255.70
Purchase #4	$151.56	11.872%	$169.5532	$169.55	$169.55	$169.60
Purchase #5	$150.77	9.128%	$164.5323	$164.53	$164.55	$164.50
Purchase #6	$136.46	5.755%	$144.3133	$144.31	$144.30	$144.30
Purchase #7	$101.33	4.265%	$105.6517	$105.65	$105.65	$105.70
7 purchase totals =	$1,068.83		$1,165.0929	$1,165.08	$1,165.10	$1,165.20