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	$80.71	12.522%	$90.8165	$90.82	$90.80	$90.80
Purchase #2	$156.39	11.797%	$174.8393	$174.84	$174.85	$174.80
Purchase #3	$118.31	4.510%	$123.6458	$123.65	$123.65	$123.60
Purchase #4	$186.65	10.654%	$206.5357	$206.54	$206.55	$206.50
Purchase #5	$191.54	3.716%	$198.6576	$198.66	$198.65	$198.70
Purchase #6	$127.84	9.556%	$140.0564	$140.06	$140.05	$140.10
Purchase #7	$50.51	11.400%	$56.2681	$56.27	$56.25	$56.30
7 purchase totals =	$911.95		$990.8194	$990.84	$990.80	$990.80