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	$123.34	9.874%	$135.5186	$135.52	$135.50	$135.50
Purchase #2	$67.83	4.867%	$71.1313	$71.13	$71.15	$71.10
Purchase #3	$189.34	8.116%	$204.7068	$204.71	$204.70	$204.70
Purchase #4	$124.33	5.578%	$131.2651	$131.27	$131.25	$131.30
Purchase #5	$183.57	11.675%	$205.0018	$205.00	$205.00	$205.00
Purchase #6	$164.70	6.506%	$175.4154	$175.42	$175.40	$175.40
Purchase #7	$46.37	13.422%	$52.5938	$52.59	$52.60	$52.60
7 purchase totals =	$899.48		$975.6328	$975.64	$975.60	$975.60