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	$110.76	11.533%	$123.534	$123.53	$123.55	$123.50
Purchase #2	$148.75	10.812%	$164.8329	$164.83	$164.85	$164.80
Purchase #3	$165.39	11.635%	$184.6331	$184.63	$184.65	$184.60
Purchase #4	$107.52	4.219%	$112.0563	$112.06	$112.05	$112.10
Purchase #5	$73.83	8.638%	$80.2074	$80.21	$80.20	$80.20
Purchase #6	$27.87	3.118%	$28.739	$28.74	$28.75	$28.70
Purchase #7	$250.45	11.611%	$279.5297	$279.53	$279.55	$279.50
7 purchase totals =	$884.57		$973.5324	$973.53	$973.60	$973.40