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	$56.56	13.846%	$64.3913	$64.39	$64.40	$64.40
Purchase #2	$100.65	7.413%	$108.1112	$108.11	$108.10	$108.10
Purchase #3	$81.79	10.492%	$90.3714	$90.37	$90.35	$90.40
Purchase #4	$235.77	12.616%	$265.5147	$265.51	$265.50	$265.50
Purchase #5	$237.53	7.757%	$255.9552	$255.96	$255.95	$256.00
Purchase #6	$181.30	7.357%	$194.6382	$194.64	$194.65	$194.60
Purchase #7	$107.72	6.212%	$114.4116	$114.41	$114.40	$114.40
7 purchase totals =	$1,001.32		$1,093.3936	$1,093.39	$1,093.35	$1,093.40